On this Guide – the list of common garden plants problems. Each bug, disease or other problem has it’s photo, description and characteristics, damage, life circle, ways to control, pesticides, and other useful information. Feel free to ask questions or share your experience in the comments.
Small (2-3mm) soft-bodied insects cluster on the tips of branches or on the undersides of leaves. They can be pinkish-white, green, brown or black in colour. Aphids may or may not have wings. Stickiness or black sooty mold on lower leaves and stems of plants usually indicates a significant aphid population higher up in the plant.
Aphids feed on a wide variety of fruit, vegetable and ornamental plants. They reduce plant vigour by sucking plant sap, and may also cause leaf curling or stunting of flowers. Aphids can transmit virus diseases from plant to plant.
Eggs overwinter and hatch in early spring into females. These give birth to live nymphs which mature into adults within a week and bear more nymphs. Once a plant is infested some nymphs develop wings and move to other plants. In the fall males appear and mate with females, which lay overwintering eggs. In some cases ants will move aphid eggs into their nests to protect them for winter. In spring they will place them back onto plants.
- Apply dormant oil and lime sulfur in March to smother overwintering eggs.
- Avoid excessive nitrogen fertilization as soft foliage will attract aphids.
- Inspect plants frequently as aphid populations rise quickly.
- Crush aphids with fingers if practical.
- Prune off and destroy infested branch tips.
- Wash undersides of leaves with a strong spray of water.
- Limit the movement of ants in trees by placing Tanglefoot around the trunk (ants ‘farm’ aphids for their sweet secretion and will protect them).
- Apply pesticides, making sure to get good contact on underside of leaves.
- Introduce Aphidoletes or Lady Beetle predators.
- Replace aphid prone plants with resistant species.
Pyrethrin, Safer’s Soap, Trounce or Rotenone at label rates.
Common ants are not destructive, in fact they help clean up debris, aerate the soil, prey on other insects and aid in pollinating some varieties of fruit as they collect nectar.
- They can become a nuisance when entering the house or if numbers get high outside.
- Some will also bite if crushed against bare skin.
- Ants like to feed on aphid secretions; they will actually ‘farm’ aphids by carrying them onto plants, tend to them and protect them from predators.
- Carpenter ants can cause structural damage to wooden homes; these ants are much larger (8 to 19 mm long). They expel sawdust from their nests and will appear indoors in spring with wings. Control of carpenter ants is most satisfactorily done by a licensed pest control company with proper equipment.
Queens lay hundreds of tiny eggs which hatch in about 30 days into blind legless larvae. There is often only one queen per nest. Some species have multiple queens per nest, however.
Female worker ants feed and care for larvae from 11 to 61 days, which then pupate for 12 to 25 days before becoming adults (female workers and males). Workers enlarge, defend and repair nests, collect food, care for the young and the queen.
- Monitor ants’ movements to determine their food source as well as their nest location.
- When the outdoor food source is aphid secretions in a tree or shrub, place Tanglefoot barrier around the tree trunk.
- If the food source is inside the house, store food and waste in tight containers, seal cracks where ants are entering and/or apply pesticide dust in cracks.
- Drench nests with boiling water or pesticide in early morning before ants are active.
- Apply liquid boric acid or set out borax traps – workers eat bait as well as carrying it back to the nest to share with the colony.
- Keep a pest journal recording food source, location of nests, controls used and when ants first became a problem.
- Chemical-Sevin at label rates (dust)
- Diazinon at label rates (drench)
- Ant Killer Dust at label rates
- Diatomaceous Earth at label rates (dust)
- Trounce at label rates (drench)
Root and Vine Weevil
Root and Vine Weevils feed on a variety of berry and ornamental plants. Larvae feed on roots and girdle stems, seriously weakening plants or causing them to die. Adults feed at night, cutting half-circle notches in leaf margins. This looks unsightly, but rarely causes serious injury. Vine weevils feed on grape bunches, causing grapes to drop off.
Weevils overwinter as larvae in soil, or occassionally as adults. Larvae pupate in soil with adults emerging in late spring. Adults begin laying eggs 1 to 2 weeks later (all adults are female), with each adult laying up to 500 eggs over a 2 to 3 week period. Eggs hatch in 10 to 20 days, with larvae feeding on roots through summer, fall, and the following spring. There is usually one generation per year.
- Check susceptible plants frequently for leaf notches, and once detected begin control measures immediately before egg-laying begins.
- Collect adults at night using a flashlight, or during the day under debris near plants.
Apply contact pesticide at night.
- Place weevil bait containing 5% sodium fluosilicate around base of plants, then try to keep the area dry.
- Reduce/remove plants prone to weevil attack.
- Keep a pest journal for next year, recording host plants, severity of damage, controls used and when you first noticed pest in relation to another plant in bloom.
Chemical – Malathion or Endosulfan at label rates.
Alternative – Pyrethrin or Rotenone at label rates.
Bronze Birch Borer
Larvae chew tunnels under the bark where the xylem and phloem meet, causing ‘girdling’ of the trunk or branch. Visible damage includes lumpy bark in upper branches or trunk as well as small sparse leaf development, yellow leaves and/or dead branches in upper portions of trees.
Larvae overwinter inside the branches and begin feeding again when sap starts to flow. Pupation also occurs inside the tree, with adults chewing a D-shaped hole in bark, emerging in June or July. Adults lay eggs in upper branches until the end of August. Upon hatching larvae bore directly into the tree. Borers may have a 1 or 2 year life cycle.
No satisfactory control is known. Pruning infected branches 30 cm below any “lumpy bark” may prolong the tree’s life, otherwise removal of the tree is inevitable. Burn all wood to destroy the larvae inside. The best control is prevention by keeping the tree adequately watered and fertilized. Borers can’t readily attack healthy trees. Heritage Birch (Betula nigra Heritage), a white-barked birch, is resistant to bronze birch borer.
Crabgrass thrives in lawns that are improperly watered and fertilized. Left unchecked it can spread to cover large expanses in the lawn.
Prevention and control
Lush and healthy lawns are always able to out-compete crabgrass. Follow a good fertilization program, irrigate less frequently but deeper, and mow the grass as high as is practical. Crabgrass seed needs high light levels to germinate, so cutting the lawn higher will shade the roots and provide less light.
Herbicides called pre-emergents will help to control crabgrass by preventing the seed from germinating. It must be applied before the seed germinates in spring to be effective. Pre-emergents are available in a granular formulation mixed with lawn fertilizer.
A post-emergent herbicide is applied to actively growing crabgrass plants. Both methods may give some control, but keeping your lawn lush and healthy with proper cultural practices will keep crabgrass from becoming established in the first place
Black Spot on Roses
The leaves become stressed and begin to turn yellow, then wither and drop off. New leaves may be produced, but these will develop black spot as well.
- Pinch off and dispose of any affected leaves as they occur.
- Keep rose foliage as dry as possible, as the disease is spread by splashing water.
- Remove leaves in late fall, and rake up fallen leaves from around the base of plants.
- Spray canes with dormant oil and lime sulfur before plants leaf out in spring.
Apply any of the following sprays:
- Bordo Copper Spray
Fungicides must be applied before the fungus becomes established to be most effective.
Caterpillars feed on many early vegetable and flower seedlings. During the day cutworms rest beside plant stems below the soil surface. At night they feed on stems at the soil line, cutting off the plant. Small seedlings are sometimes completely eaten.
Cutworms overwinter as pupae or eggs which emerge on the first warm spring days. Adults lay eggs during May. Eggs hatch in 5 to 7 days. Caterpillars feed on grass and other plants for 3 to 5 weeks, then pupate in soil. Adults emerge in late August to early September, feed on plant nectar, and lay eggs. There is usually one generation per year.
- Removing crop residue in the fall and keeping soil weed-free during winter reduces egg-laying sites and starves newly hatched cutworms.
- Prevent damage by placing collars (eg. tin cans, milk cartons, toilet paper roll) around young seedlings. Push the collar into the soil so it is half-buried.
- Apply pesticides.
- Keep a pest journal for next year, recording type of seedlings damaged, location in garden, and controls used.
- Scatter Cutworm Bait (bran containing Sevin) in late afternoon after planting.
- Scatter moist bran mixed with molasses and BTK (Bacillus thuringiensis var. kurstaki) in the afternoon a week before planting.
Deer are very adaptable creatures and, although they have their favourite plants, they will feed on almost any plant, especially during snowy winters when natural vegetation is covered. Several methods can be tried to minimize damage to the home garden in areas where deer are prevalent
Repellents can be effective, but usually for short periods of time. Multiple applications are often necessary, depending on how much rain falls and how hungry the deer are. Commercial repellents such as Thiram are available.
Home-made repellents can also be effective-bars of soap hung in branches, human hair, dried blood (Blood Meal) and hot sauces are among the more popular methods which have been tried.
Homeowners often come up with ideas that are unique to their situations. Motion-sensing scare devices will sometimes work. Deer will adapt to almost any situation short of a fence, so it’s best to try different ideas to keep them off their guard.
Blossom End Rot
Blossom end rot is not caused by a bacteria or a fungus, but by a deficiency of calcium, and an uneven water supply in the soil. More calcium is required by developing fruit than by the leaves or stems. When plant growth – which has been slowed by a lack of water – begins again, there is not enough calcium absorbed to enable fruits to develop properly. Blossom end rot is more common on earliest set fruits.
Prevention and control
- Maintain uniform soil moisture during the growing season.
- Water deeply, and apply a mulch around the base of the plants.
- Liquid calcium can be applied in a spray form to foliage.
- Turf within the rings will turn yellow and appear dead.
- Fairy rings and mushrooms usually appear in soils that contain decomposing organic material.
- Tree roots, sawdust, or bark mulch can be sources.
Prevention and control
- Apply adequate nitrogen to soil. Mushroom rings and other similar problems are often related to soil infertility and imbalance of the microbial activity in soil.
- Aerate the affected area to ensure better water penetration, then water heavily. Mushrooms can be raked off and removed.
When fairy ring is firmly established elimination may be difficult without removing the affected sod and soil beneath.
Leafhoppers feed on many fruits, vegetables and ornamentals, particularly grapes, roses, and Virginia creeper. Both nymphs and adults suck plant sap from stems and undersides of leaves, reducing plant vigour as well as lowering flower and fruit production. They also inject a toxic saliva which causes white mottling, tipburn and curling of leaves. Leafhoppers can transmit virus diseases from plant to plant.
Some species overwinter as eggs on bark of various plants, others as adults under debris and still others migrate south for winter. Feeding begins in early to mid-May by newly hatched nymphs as well as overwintering and returning adults. Wingless nymphs develop for several weeks before molting into winged adults. Adults lay eggs 2 to 3 weeks later, these hatch in 10 to 14 days. Some species have only one generation per year, other have 2 or 3 a year.
- Clean up plant debris in fall to reduce overwintering adults.
- Apply dormant oil in March on host plants, as well as neighbouring plants, to smother overwintering eggs.
- Inspect plants frequently, beginning in early May, when grape leaves are about half size, by brushing with hands and watching for leafhoppers.
- Apply pesticides, making sure to get thorough coverage on the undersides of the leaves.
- Keep a pest journal for next year, recording host plants, controls used and when you first noticed pest in relation to another plant in bloom.
Alternative – Pyrethrin, Safer’s Soap, Trounce or Rotenone at label rates in early morning or evening when leafhoppers are less active.
Potassium Salts of Fat. Acid, Pyrethrin.
Honey Locust Pod Gall
Adult midges are small black flies about 3 mm long. Larvae are whitish-yellow worms about 6 mm long. They are found inside leaflet galls.
Several varieties of Honeylocust (Gleditsia) are affected. Larvae cause leaflets to form into a pod which often turns reddish in colour and sometimes drops prematurely. Smaller branches often die and even though trees are not greatly distressed, their ornamental value is lessened.
Insects overwinter as adults, although it is not known where. Adults fly and lay lemon coloured eggs in spring when new growth begins. Larvae emerge in 1 or 2 days and immediately begin to feed, causing the leaflet to develop around them into a pod. Larvae pupate inside the pod and emerge as adult midges. There are several generations per year, appearing at 3 to 4-week intervals.
- Inspect plants frequently for adult midges (yellow sticky traps may help) and leaflet galls (larvae).
- Prune off and destroy gall-infested branch tips. Pesticide application is only moderately effective.
- The best results are obtained when midges are flying, larvae are newly hatched and leaflets are opening in spring, before the galls are formed.
- Keep a pest journal recording the number of generations observed and timing of sprays.
Pyrethrin, Safer’s Soap, Trounce or Rotenone at label rates every 3 days whenever midges are flying.
Larvae are very large (up to 10 cm) caterpillars with diagonal white stripes and a short horn at the tail. Adults are large (up to 12 cm) grey or brown fast-flying hawk moths, sometimes mistaken for hummingbirds.
Larvae consume large amounts of foliage, as well as fruit, leaving dark droppings on leaves. Most feeding is done at night.
Hornworms overwinter as dark brown pupae in soil. Adults emerge in late spring and lay eggs on the undersides of tomato leaves. Eggs hatch in 5 to 7 days, with larvae reaching full size in 3 to 4 weeks. There are 1 or 2 generations each year.
- Cultivate top 15 cm of soil in early spring to kill pupae.
- Handpicking is very effective. If handpicking is not practical, apply pesticide when caterpillars are very small.
Chemical – Sevin at label rates.
Alternate – BtK (Bacillus thuringiensis var. kurstaki) or Rotenone at label rates.
Tiny (1.5 mm) greyish-white round discs on needles and twigs. They move very slowly or not at all.
Juniper scales suck sap from juniper foliage, causing plants to initially look off in colour. As the infestation progresses individual branches will turn grey or yellow, drop needles and produce little new growth. Finally, large portions or the entire plant will die.
Scales overwinter as full-grown fertilized females. Each female lays up to 40 eggs in May, which hatch over a 30 day period from late May to late June. Crawlers disperse over the whole plant and begin feeding. They are light enough even to be blown by wind to other junipers. Crawlers develop rapidly with females molting 3 times and males 5 times. In late summer and early fall tiny winged adult males seek out and mate with adult females. There is only one generation per year.
- Apply dormant oil and lime sulfur in March to kill overwintering females.
- Inspect junipers regularly for scale.
- Prune off and destroy badly infested branches.
- Apply pesticides thoroughly. Juniper scale are protected by armoured shells, making control difficult.
- Infested plants should be removed and replaced with a species other than juniper.
- Safer’s Soap or Trounce at label rate, first in late May, again in mid-June, and finally in early July.
- Summer Horticultural Oil in early June.
Late Blight On Tomatoes
Late blight is a fungus that occurs not only on tomatoes, but on potatoes, peppers, and eggplants as well. The first symptoms are brown or black lesions on stems and blotches on leaves. A grey fuzzy mold then develops. Fruit may develop a brown or black leathery rot, then become soft and mushy.
Late blight spreads in cool, wet or humid weather. The spores can move in wind-blown rain, in groundwater, runoff or in water splashed from plant to plant in the garden. This disease has only become a problem in the Interior in the past few years, but it is escalating.
- Grow tomatoes in a warm, dry sunny area.
- Water the soil, do not apply water to leaves or fruit.
- Remove any diseased foliage at the end of the growing season to prevent the disease from carrying over.
- Immediately remove diseased leaves or shoots. Do not compost them.
- Destroy any volunteer tomato or potato plants in the garden.
Apply copper spray at label rates after planting and before the disease occurs.
Adults are black sawflies 2 to 3 mm long. The flat yellowish-white larvae, about 6 mm, are seldom visible.
Larvae tunnel between the leaf surfaces, producing irregularly-shaped brown lines or blotches. Leaves of severely affected trees appear scorched by fire. Grey, white, and paper birch are most affected.
Pupae overwinter 2 to 5 cm below the soil surface. Adults emerge in spring when leaves are half grown. They hover over birch trees, laying one egg per leaf, usually near branch tips. Eggs soon hatch and larvae mine the leaf for 10 to 15 days. Mature larvae then cut a hole through the leaf, drop to the ground where they pupate for 2 to 3 weeks. There are 2 to 4 generations per year.
- If practical remove affected leaves by hand. Plant Black, European or River birch to prevent leafminer damage, as they rarely feed on these species.
- Inspect tips of birch branches for sawflies when leaves are about half open. If insect is present, applying contact pesticides can help reduce numbers.
- Keep a pest journal for next year including severity of damage, controls used, and when you first noticed pest.
Chemical – Malathion at label rates (contact pesticides).
Alternative – Safer’s Soap, Trounce or Summer Oil at label rates (contact pesticides).
Larvae are 2 to 3 cm green caterpillars with brown heads, usually found inside rolled leaves. Adults are 1 to 2 cm mottled brown moths.
Leafrollers feed on fruit as well as ornamental trees and shrubs. Larvae roll leaves around them using silk, then feed on enclosed buds, leaves and fruit.
Eggs overwinter on tree bark and hatch in early spring. Larvae feed about one month, then pupate inside rolled leaves or on bark. Adults emerge in late June or July to lay overwintering eggs. There is one, and often two, generations per year.
- Apply dormant oil in March to smother overwintering eggs.
- Inspect plants frequently for tiny green caterpillars before they begin to roll leaves.
- If practical, remove caterpillars by hand.
- Apply pesticide just after new growth opens on ornamentals, and just after petal fall on fruit before young larvae begin to roll leaves.
- Keep a pest journal for next year, recording host plants, controls used and when you first noticed pest in relation to leaf/fruit emergence or another plant in bloom.
Btk (Bacillus thuringiensis var. kurstaki), Pyrethrin or Rotenone at label rates.
Spider mites are tiny insects (from 0.1 to 1 mm long) with fine hairs, eight legs, and no wings. They can be yellow, red, green, dark brown or spotted. Fine webbing on plant foliage usually indicates spider mite presence.
There are several species of spider mites which feed on many different houseplants, fruits, vegetables and ornamentals. Both nymphs and adults suck plant sap, causing reduced plant vigour and small fruit with russeted skin. Leaves first develop a bleached look, then a bronzy appearance and finally become brown and brittle, accompanied by extensive webbing. Damage on outdoor plants is most visible between July and September.
Some species overwinter as eggs, others as adults under debris. In early spring, as the weather warms, adults crawl or are blown onto plants to lay eggs. Nymphs emerge in 2 or 3 days, then develop into adults in 7 to 10 days. There are many generations per year, with life cycles taking only 7 to 10 days in hot dry weather.
- Inspect plants frequently, especially the undersides of middle-aged leaves along the main ribs, using a 10x magnifying lens. It may be helpful to shake foliage over a white sheet of paper to catch any mites.
- Apply dormant oil and lime sulfur in March.
- Frequently mist plants which are prone to mites with a fine water spray.
- Introduce Phytoseiulus predatory mites.
- Apply pesticides.
- Keep a pest journal for next years, recording host plants, controls used, and when you first noticed pest in relation to other plants in bloom.
- Summer Oil at label rate. Can be repeated in six weeks.
- Three applications of Safer’s Soap or Trounce at label rates five days apart.
Leatherjacket or Crane Fly
Adults are large (2 cm. long) mosquito-like flies, appearing in August and September. Larvae are grey legless worms varying from 3 mm to 2.5 cm long, spending most of their life in the top 2.5 cm of the soil.
Larvae feed on roots of grasses and legumes, causing plants to weaken or die. When sufficient larvae are present lawns develop irregular-shaped yellow patches.
Leatherjackets overwinter as young larvae. As soil temperatures increase in March through May, larvae feeding accelerates (as does damage). Larvae reach their full size by mid-June before pupating in July. Adults emerge in August, laying eggs through into September. Eggs hatch in about two weeks, with young larvae doing little damage before winter.
- Ensure a healthy lawn through proper care. To monitor leatherjacket populations, remove a 15 cm by 15 cm piece of sod 5 cm deep in early May.
- Submerge in a salt solution for five minutes. If more than five larvae surface, a pesticide should be applied before May 31.
- Control is not necessary in fall as many larvae usually die over winter.
- Keep a pest journal for next year, including location and severity of damage, controls used and when damage was first noticed.
Chemical – Malathion at label rates once between October and May when the ground is not frozen.
Alternative -none recommended.
Peach Leaf Curl
Infected buds on peaches and nectarines produce leaves in spring with a reddish tinge, a thick, crisp texture, and curled growth. Leaves become powdery grey in colour, then turn yellow or brown and fall off.
This fungus disease is more prevalent when spring weather is wet and cool. Early leaf drop causes weakening of the tree, making them more susceptible to other diseases, and causing reduced yields.
Prevention and Control
- Rake up and destroy or dispose of fallen leaves, and prune off damaged leaves or twigs in spring.
- Apply dormant spray (Dormant oil and Lime Sulfur) during the dormant season.
- Copper Spray should be applied in September, and again in early spring.
- Fertilize trees which have to lost foliage to increase vigour.
This fungus attacks a wide variety of plants, and is particularly troublesome on roses. It appears as a white powdery film on leaves and shoots. Powdery mildew can cause reduced plant vigour, distorted growth and chlorosis. If left unchecked powdery mildew can cripple a plant.
Environmental conditions can cause mildew diseases. They are favoured by dry weather with warm days and cool nights. Cultural practices such as trimming and fertilizing which stimulate and prolong succulent plant growth will encourage many powdery mildew strains.
- There are many plant varieties which are more resistant to powdery mildew.
- Try to ensure good air circulation around plants.
- Trim off affected growth as it occurs.
Spray with a fungicide available for use against powdery mildew:
Fungicides must be applied before the fungus becomes established to be most effective.
Soft-bodied muscular mollusks (not insects) which move on a large flat foot, leaving a slimy trail of mucus. Slugs can be orange, grey, brown or black. They are most active at night or during wet weather.
Slugs feed on a wide variety of plant foliage, “rasping” irregular-shaped holes causing leaves to look tattered. They can also completely eat seedlings and damage blossoms on flowering plants.
Adults lay egg clusters in moist soil under stones or debris. Eggs hatch in 2 to 4 weeks, with slugs growing for 5 to 24 months before reaching sexual maturity.
- Reduce moisture level in garden and remove debris or other daytime hiding places.
- Reduce or remove plants prone to slug attack.
- Protect seedlings using a barrier of wood ashes or diatomaceous earth (try to keep dry).
- Copper-backed paper stapled to boards works well also.
- Collect slugs at night using a flashlight.
- Place wood, cabbage leaf, overturned pots, inverted grapefruit half traps, or a small amount of beer in a container in the garden. Check during days and destroy slugs.
- Place slug bait containing Metaldehyde in areas where slugs are evident.
- To protect animals, put bait under rocks or in a bait protector (inverted coffee can with holes along bottom).
Spruce Gall Adelgid
Most forms of spruce gall adelgid are seldom visible. Cone-like galls at the tips of spruce branches is usually the first sign of the pest’s presence.
Adelgids feed on Colorado, Norway, Alberta, Engelmann and White Spruce as well as Douglas Fir. On Douglas Fir needles turn yellow, become distorted and drop, with black sooty mold often developing, with no galls forming. On spruce 2.5 cm to 5 cm green to purple cone-shaped galls form on branch tips, killing new shoots. Galls later turn brown and remain on the tree for several years.
Spruce gall adelgid requires both Douglas Fir and Spruce trees to complete its rather complicated life cycle. On spruce tiny greyish nymphs overwinter on the underside of branches. They mature into adult females in early spring and lay several hundred eggs on branch tips. Eggs hatch just as new growth begins. Nymphs then feed, causing tips to swell into many chambered galls. After about 2 months of feeding galls turn brown, open and nymphs emerge. Nymphs then transform into adult females and fly to Douglas Fir or another spruce to lay eggs.
On Douglas fir females lay eggs in August on the lower surface of current season’s needles. Eggs hatch by September and nymphs settle on the underside of needles to overwinter. The following spring nymphs become adult females, lay eggs (enveloped in white fuzz) which give rise to both winged and wingless female adelgids by summer. The wingless form remains to feed on Douglas fir, and lays eggs that hatch into overwintering nymphs. Winged forms fly to spruce where they lay eggs that develop into overwintering nymphs.
- Apply dormant oil in March, making sure to get good contact on the undersides of branches, to kill overwintering nymphs on both spruce and Douglas fir. Do not use oil on blue spruce.
- Apply pesticides just as new growth opens on spruce and in mid- August on Douglas fir.
- Inspect spruce frequently for galls, and, if practical, handpick green galls before they open.
Safer’s Soap, Trounce, Rotenone or Summer Oil at label rates. Do not use oil on blue spruce.
Larvae are very small (1 to 2 mm long). They can be yellowish or orange. Adults are hard to see as they fly when disturbed. The dots of black excrement and the damage they cause are usually more visible than the thrips themselves.
Thrips feed on a variety of houseplants, vegetables and ornamentals, particularly roses, peonies, gladiolus and chrysanthemums. Both larvae and adults feed by rasping plant tissue and sucking the juice, causing a silvery appearance on leaves, tattered or streaked flowers and deformed fruit. Thrips usually cause little damage, however severe infestations can stunt plants, shorten bloom period, prevent flowers from opening and reduce crop yields. Thrips may also transmit virus diseases from plant to plant.
Most thrip species overwinter as pupae in the soil, with adults emerging to feed about the time leaves on Linden trees start to open. Adult females insert several hundred eggs into stem, leaf or flower tissue. Larvae hatch in 3 to 5 days, feed for several weeks and then drop to the soil to pupate. Adults emerge 1 to 2 weeks later. There are between 1 and 8 generations per year, with the life cycle taking only 3 weeks for some species.
- Hang blue or yellow sticky cards on susceptible plants and inspect frequently for insects, damage or excrement.
- Water thoroughly when irrigating to drown pupae in soil.
- Apply pesticides to affected plants.
- Keep a pest journal for next year, recording host plants, controls used, and when you first noticed a pest in relation to another plant in bloom.
Pyrethrin, Safer’s Soap or Trounce at label rates. Dust plants and soil around affected plants with diatomaceous earth.
Verticillium wilt affects several different types of trees and shrubs. This fungus can remain dormant in soil for many years. When roots of susceptible plants grow near, the fungus infects the roots and grows upward into the water-transporting system of the plant, blocking the movement of water.
Symptoms can range from yellowing of the foliage, leaf scorch, and sparseness of foliage, to rapid wilting, and dying of leaves and branches. Symptoms can occur on one branch or section of plant only, or the entire plant can die, especially during periods of hot, dry weather.
Internal symptoms of the disease are streaks or bands of dark sapwood underneath the bark. This can be seen by cutting diagonally across the base of an infected branch.
Prevention and control
Plants that quickly wilt and dry throughout cannot be saved. Affected single branches can be removed. This may, but not always, be enough to halt the spread of the disease. Keep affected plants adequately watered, and fertilize with a balanced fertilizer. Certain trees and shrubs are more resistant to verticillium wilt. Turn this page over to see the list.
Larvae are slender yellow hard-bodied worms up to 3 cm long. Adults are brown or black flattened click beetles up to 3 cm long.
Wireworms feed on a wide range of vegetables and flowering plants. Seedlings wilt and die, root crops are tunneled.
Overwintering adults lay eggs in plant roots in spring. Larvae hatch in 3 to 10 days, feeding near soil surface during spring and fall, moving deeper in summer and winter. Larvae feed for 2 to 6 years before pupating in late summer. Usually all stages are present in an infested area.
Grassy areas dug up and planted for the first time often have wireworm problems. Cultivate thoroughly once a week for 4 to 6 weeks in fall to destroy larvae and allow birds to feed. Test for wireworms in March or April using pieces of potato or whole wheat flour buried 10 cm in the soil (one for every 10m2 of a garden). Mark each site with a stake and check 3 to 5 days later.
Walnut Husk Fly
Adults are tawny brown, 4 to 6 mm long (slightly smaller than a housefly) with large green eyes, banded wings, and a yellow spot of their back. Headless larvae are white when young, turning yellow as it matures, up to 13 mm in length.
Larvae tunnel into green walnut husks, producing a slimy black mush that stains the walnut shell (does not affect the nut). Occasionally peaches grown close to walnuts will be attacked. Larvae feed internally in peach flesh.
Overwinters as pupa in soil beneath walnut trees. Adults emerge from July to September and mate 8 days after emergence. Eggs hatch in 5 days and maggots feed for 3 to 5 weeks. Mature larvae exit the fruit and drop to the soil to pupate where they remain at least one year, and sometimes up to 3 or 4 years. There is one generation per year.
- Monitor adults using sticky yellow board traps. Hang traps at least 6 feet off the ground in a shady part of the tree. You can also hang a smooth lime green ball the size of a tennis ball coated in Tanglefoot.
- Once a significant number of adults are detected, usually early to mid-August, apply contact pesticide within 10 days to prevent egg-laying. Repeat 3 to 4 weeks later. Do not apply after husks split.
- Pick off damaged fruit if practical. Remove fallen infected fruit and submerge in a bucket of water to drown remaining maggots.
- Keep a pest journal for next year, noting the severity of damage, controls used, and when you first noticed pest in relation to fruit emergence or bloom time of another plant.
Chemical – Malathion or Ambush at label rates.
Alternative – Safer’s Soap, Trounce or Pyrethrin at label rates.
Adding molasses significantly increases effectiveness of pesticides.
Delicate, powdery white 1 to 3 mm insects, found on the underside of leaves of fluttering around plants. Stickiness or sooty mold on lower plant leaves usually indicates a significant whitefly population.
Whitefly feed on many different houseplants, fruits, vegetable and ornamental plants. Nymphs and adults both suck sap, reducing plant vigour and causing pale, yellow or wilted leaves. Whitefly can transmit viruses from plant to plant.
Some whitefly species can overwinter outdoors as nymphs or pupae, all species overwinter indoors or in greenhouses. Females lay 200-400 yellow eggs in a circle on the undersides of leaves. Nymphs hatch in 3 to 10 days, crawl for several hours, then lose their legs and settle to feed until they pupate. Adults emerge within a week and repeat the cycle. There are numerous generations per year, with the life cycle taking 25 days at 20 deg. C and only 18 days at 27 deg.
- Inspect undersides of plant leaves frequently. Yellow sticky traps are also helpful.
- If practical crush whitefly with fingers or vacuum in early morning when insects are less active.
- Apply pesticides, making sure to get good contact on the undersides of the leaves.
- Introduce Encarsia formosa parasitic wasps.
- Replace plants prone to whitefly with resistant species.
- Keep a pest journal for next year, recording host plants, controls used, and when you first noticed pest in
- relation to other plants in bloom.
Alternative-3 applications of Pyrethrin, Safer’s Soap, Trounce or Rotenone at label rates three days apart, making sure to get good contact on the underside of leaves.
Plant diseases have much more potential for damage to our landscapes than do insects, and are much more difficult to control once they strike. For this reason most control strategies are of a preventive nature:
Resistant plants and plant varieties:
Study garden encyclopedias, seed and plant catalogs, and talk to nursery people and horticulturists when planning additions to your garden. Choose those plants found to be the most resistant to disease in your climate. Native plants are nearly always the most resistant to disease in our area.
In the vegetable garden, rotating your crops (not planting the same vegetable family in the same spot 2 years in a row) is a good disease avoidance procedure.
Good air circulation is important to many types of plants.
Avoid overhead watering late in the day. Plant leaves that stay damp all night develop fungal diseases more readily.
Diseased plants should not be left around the yard or put in the compost. Burn them or put them in the garbage.