Pests, Hail and Other Problems
Hail, wind, hungry jackrabbits and a hot week full of flea beetles: every Lethbridge gardener meets them sooner or later. This page helps you work out what went wrong and fix it with nothing more than your hands, a hose, a row cover and a bit of planning. No sprays, ever.
On this page
What’s wrong with my plant?
Answer a few questions to find the likely cause and a natural fix.
Plant doctor
Our approach: no sprays
This garden guide doesn’t recommend sprays of any kind: no pesticides, no fungicides, no weed killers, and no “natural” or homemade sprays either. That isn’t because every spray is dangerous. It’s because a home garden almost never needs one, and sprays tend to kill the ladybugs, lacewings, hoverflies and bees that do most of the pest control for free.
The one “spray” we do use is a strong blast of water from the hose. It knocks aphids and spider mites off plants, and most of them never find their way back.
Everything else on this page is physical: covering plants, fencing, picking pests off by hand, trapping, pruning, and growing healthy plants in good soil. It sounds old-fashioned. It works.
What it means for you: a few holes in a leaf are not a problem. A plant can lose a surprising amount of leaf before the harvest suffers. Act when damage is spreading fast or threatens seedlings, and accept a little sharing with the bugs.
Hail: protection and recovery
Alberta gets some of the most frequent damaging hail in Canada, and in Lethbridge the season runs mainly from June to August. Most storms come in the afternoon or evening, when hot, unstable air builds thunderclouds over the foothills and they drift east toward the city. A five-minute storm can shred a garden that took three months to grow.
Before the storm
- Watch the sky and the forecast. Environment and Climate Change Canada issues severe thunderstorm watches and warnings that mention hail. Check the forecast page on hot, humid afternoons.
- Keep covers handy. Buckets, laundry baskets, cardboard boxes, old blankets and lawn chairs set over small plants all work in a pinch. Weigh light ones down; hail usually comes with a strong gust.
- Build a hail frame for prized beds. Hoops or a simple wooden frame over a raised bed, with garden netting or shade cloth stretched over it, stops most hail and also cuts wind and harsh sun. Leave it on from June to August. The finer the mesh, the smaller the hail it stops.
- Bring pots and hanging baskets in or tuck them under the eaves.
After the storm
- Wait a day before judging. Hail damage always looks worse in the first hour. Let plants dry and perk up.
- Leave torn leaves on. A shredded leaf still makes food for the plant. Only remove leaves that are completely broken off or rotting.
- Cut broken stems cleanly just below the break, so the plant can heal and send out new shoots.
- Check the growing tips. If the top bud of a tomato, pepper or squash survived, the plant will usually recover within two or three weeks. Lettuce, chard, kale and herbs regrow from the base.
- Water and feed lightly. A drink and a side-dressing of compost help regrowth.
- Use bruised fruit soon. Dented tomatoes, apples and zucchini are fine to eat but won’t store.
- Replant if it’s early enough. Until about late June, there’s still time to resow beans, lettuce, radishes, beets, spinach and other quick crops.
Trees and shrubs: hail can tear bark on young trees. Don’t paint or seal the wounds; trees heal best on their own. Trim off ragged bark edges with a clean knife and keep the tree watered. Large hail wounds on apples and mountain ash are an entry point for fire blight, so watch those trees for the next few weeks (see diseases).
Wind, sunscald and frost
Wind
Our wind tears leaves, snaps stems, and dries plants out faster than the heat does. Leaf edges that turn brown and crispy, especially on the west side of a plant, are a classic Lethbridge sign. Newly planted seedlings can be twisted off at the soil line in a single afternoon.
- Plant tall, sturdy crops or a fence on the west and southwest side of the garden as a windbreak.
- Stake tomatoes, peppers, dahlias and sunflowers when you plant them, not after they flop.
- Shelter new transplants with a board, a bucket with the bottom cut out, or a ring of row cover for their first week.
- Water more often on windy days; wind can dry out pots in hours.
Sunscald
Our high-elevation sun is strong. Peppers and tomatoes that lose leaves (to hail, disease or pruning) can get pale, papery, sunken patches on the side of the fruit facing the sun. Keep enough leaves on to shade the fruit and don’t over-prune.
Young trees get a winter version: on bright February days, sun warms the bark on the southwest side of the trunk, then it freezes hard at night. The bark cracks and splits. Wrap young, thin-barked trees (maples, lindens, fruit trees) with a light-coloured tree wrap or guard from late fall to spring, and remove it during the growing season.
Winter burn on evergreens
Spruce, pine, juniper and cedar can turn brown on the windward or sunny side in late winter. Their needles lose water on warm, windy chinook days while the roots are still in frozen ground. Water evergreens deeply in fall before freeze-up, and again during a dry, mild spell in winter if the ground thaws. Brown needles usually won’t green up, but buds often survive and push new growth in June.
Frost
Blackened, water-soaked leaves the morning after a clear, calm night are frost damage. See frost dates and warnings for how to protect plants and what to do the morning after.
Insect pests
These are the insects Lethbridge gardeners meet most. Our dry climate is actually a help: slugs and many fungal problems that plague wetter places are much less common here. The trade-off is that pests that love hot, dry weather, like flea beetles, spider mites and grasshoppers, can be bad in some years.
| Pest | What you see | Natural fixes |
|---|---|---|
| Aphids | Clusters of tiny green, black or grey insects on new growth and under leaves; curled, sticky leaves; ants running up and down the plant. | Blast them off with the hose every few days. Squish small clusters. Encourage ladybugs, lacewings and hoverflies. Go easy on high-nitrogen fertilizer, which produces the soft growth aphids love. |
| Flea beetles | Tiny black beetles that jump when disturbed; leaves peppered with small round “shot holes,” worst on radishes, arugula, cabbage family, potatoes and eggplant in hot, dry spring weather. | Cover with row cover right at seeding or transplanting and seal the edges. Keep seedlings watered so they outgrow the damage. Plant a radish or mustard trap crop nearby. Bigger transplants handle the damage better than tiny seedlings. |
| Imported cabbageworm | White butterflies fluttering over the cabbage patch; velvety green caterpillars the colour of the leaf; ragged holes and dark green droppings in broccoli and cabbage heads. | Row cover keeps the butterflies off. Check under leaves weekly for tiny yellow eggs and caterpillars and pick them off. Small parasitic wasps attack them too, so keep flowers nearby. |
| Root maggots | Radishes, turnips and young cabbage-family plants wilt on a hot day; small white maggots and tunnels in the roots. Onion maggots do the same in onions. | Cover right after seeding or transplanting, before the flies arrive. Put a square of cardboard or tar paper, slit to the centre, snugly around transplant stems so flies can’t lay eggs at the base. Rotate crops. Pull and bin infested plants. |
| Cutworms | Young transplants cut off cleanly at the soil line overnight. | Put a collar around each transplant: a toilet-paper roll or a strip of cardboard pushed 2 to 3 cm into the soil. In the morning, dig gently around a cut plant to find the grey-brown caterpillar curled in a “C” and remove it. |
| Spider mites | Fine pale speckling on leaves, leaves turning bronze or dusty-looking, and fine webbing in bad cases. Worst in hot, dry spells and on beans, cucumbers, tomatoes, evergreens and houseplants summering outdoors. | Spray the undersides of leaves hard with the hose every couple of days in hot weather. Keep plants well watered. Remove badly infested leaves. |
| Grasshoppers | Big ragged bites from leaf edges, worst in hot, dry years and in gardens next to open fields and dry grass. | Row cover over prized crops in a bad year. Hand-pick in the cool early morning when they’re sluggish. Birds love them. Grasshoppers lay eggs in undisturbed soil in late summer, so lightly working bare garden soil in fall exposes some egg pods. |
| Slugs | Ragged holes and slime trails on lettuce, hostas and strawberries, mostly in wet springs or heavily watered, shady spots. | Set traps: a shallow dish of beer sunk to the rim, or a board laid on the soil and lifted each morning to collect the slugs underneath. Hand-pick at dusk. Water in the morning, not evening. |
Row cover is your best friend. Lightweight floating row cover (spun fabric) lets in light, rain and air but keeps out flea beetles, cabbage butterflies, root maggot flies and grasshoppers. Lay it over hoops, bury or weigh the edges all the way around, and put it on the day you plant, before pests find the crop. Take it off squash, cucumbers and other crops that need bees once they flower.
A run of hot, dry, windy days in May and June is flea beetle weather, and a hot, dry summer that follows a dry year tends to bring grasshoppers. Alberta Agriculture publishes a grasshopper forecast map each year based on late-summer surveys. Keep an eye on the forecast and get covers on early when a warm, dry stretch is coming.
The garden’s own pest control
For every pest in a garden, something else wants to eat it. A garden with flowers, a little water and no sprays gradually builds up its own army.
Lady beetles
Adults and their larvae eat aphids by the hundreds. The larvae look nothing like the adults: they’re small, dark, spiky and shaped a bit like tiny alligators, often with orange spots. Learn to recognize them so you don’t squish them by mistake.
Lacewings and hoverflies
Green lacewing larvae and hoverfly larvae are serious aphid eaters. The adults feed on nectar and pollen, so plant sweet alyssum, dill, yarrow, calendula and other small, open flowers. See companion planting.
Birds
Sparrows, robins and many other birds feed caterpillars and grasshoppers to their young. A birdbath, a shrub or two for cover, and leaving some seed heads standing in fall all help.
Ground beetles and spiders
Fast, dark beetles that hide under boards and mulch hunt cutworms, slug eggs and root maggot eggs at night. Spiders catch flying pests. A bit of mulch and an untidy corner give them a home.
The great ladybug hunt. Ladybugs (lady beetles) are hungry hunters. One ladybug can eat dozens of aphids in a day, and their babies (larvae) are even hungrier.
Wonder: Ladybug babies don’t look anything like ladybugs. Why might a baby insect look so different from its parent?
Try this: On a warm afternoon, take a magnifying glass (never look at the sun through it, or leave it lying in the sun) and slowly check 10 plants in the garden or park, especially plants with aphids. Count the adult ladybugs, the spiky little larvae, and the yellow egg clusters. Write down how many spots the adults have. Go back in a week and count again. Are there more aphids or fewer? Look, but don’t pick them up; let them get back to work.
Rabbits, deer, gophers and birds
Rabbits and jackrabbits
White-tailed jackrabbits are common all over Lethbridge. They mow down lettuce, beans and peas in summer, and in winter they chew the bark of young trees and shrubs above the snow line. Fence vegetable beds with chicken wire at least 60 cm high, buried 10 to 15 cm deep. Wrap young tree trunks with a wire or plastic guard in fall, tall enough to stay above deep snow.
Deer
Mule deer and white-tailed deer move through the river valley and coulees and into nearby yards, especially in West Lethbridge and along the coulee edges. They browse tulips, hostas, fruit trees, roses and almost any vegetable. A fence about 2.4 m tall is the only reliable answer for a whole yard. Netting over individual shrubs and fruit trees, and planting less-tasty plants near the coulee, help in between.
Richardson’s ground squirrels
Our “gophers” live in colonies in open grassland and come out of hibernation in late winter. In yards on the edge of open land they dig burrows and eat seedlings. Alberta classes them as a nuisance species. Garden fixes: raised beds lined underneath with hardware cloth, fencing buried at least 30 cm, and keeping a strip of taller grass rather than short lawn at the edge of the garden, since they prefer open ground with a clear view. Hawks, badgers and weasels are their main predators. Check City of Lethbridge rules before trapping in town.
Voles
Voles look like short-tailed mice. Under snow, they chew bark around the base of young trees and shrubs, sometimes all the way round, which kills the plant. In fall, pull mulch and long grass back from tree trunks and put a hardware-cloth guard around the base, pushed a few centimetres into the soil.
Magpies and fruit-eating birds
Magpies, robins and waxwings know exactly when your cherries, saskatoons and strawberries are ripe, usually a day before you do. Cover fruit with netting as it starts to colour. Pull the netting tight and fasten it at the bottom so birds can’t get tangled in it, and check it daily. Pick promptly.
Please don’t feed the deer. Feeding brings more deer into town, where they get hit by cars and can become aggressive, especially does with fawns in early summer. It also brings them straight back to your garden.
Plant diseases and look-alikes
Our dry air keeps many diseases in check, but a few are common here. All of these are managed without sprays.
Powdery mildew
A white, flour-like coating on the leaves of squash, cucumbers, peas, lilacs, roses, phlox and bee balm, usually in late summer when warm days are followed by cool, damp nights. Give plants room for air to move, water the soil instead of the leaves, and choose mildew-resistant varieties. Remove the worst leaves. On squash in late August, it mostly just signals the end of the season.
Black knot
Hard, black, sausage-shaped swellings on the branches of chokecherries (including the purple-leaved ‘Schubert’), Mayday trees, plums, cherries and other Prunus. It’s a fungus, and it spreads in spring rain. Alberta Agriculture’s advice: prune it out in late fall, winter or very early spring when the tree is dormant and the knots are easy to see, cutting at least 15 to 20 cm below each knot. Destroy the prunings right away (burn where allowed, bury, or take them to the landfill), because cut knots can keep releasing spores for months. Clean your pruners between cuts.
Fire blight
A bacterial disease of apples, crabapples, pears, mountain ash, cotoneaster and saskatoons. Leaves and shoot tips suddenly turn brown or black as if scorched, but stay on the branch, and young shoots bend over in a “shepherd’s crook.” Prune out infected branches well below the visible damage (20 to 30 cm into healthy wood), ideally in winter when the bacteria are inactive. Disinfect pruners after every cut (1 part bleach to 3 parts water, or rubbing alcohol; wear gloves and keep it away from children). Don’t compost the prunings or keep them as firewood. Avoid heavy nitrogen fertilizer, which pushes the soft growth fire blight loves.
Dutch elm disease
A fungus spread by elm bark beetles that kills elm trees. Alberta works hard to keep it out, and every elm owner has a part to play:
- Don’t prune elms from April 1 to September 30. That’s the provincial pruning ban, because fresh cuts attract the beetles. Prune between October 1 and March 31.
- Don’t store or move elm firewood. It’s illegal to keep elm wood with the bark on, and to bring elm wood into Alberta from infected provinces.
- Report a suspect tree. If the leaves on one or more elm branches suddenly wilt, yellow and brown in summer, call the STOPDED (Society to Prevent Dutch Elm Disease) hotline at 1-877-837-ELMS (3567), or contact the City of Lethbridge.
Blossom end rot (not a disease)
A dark, leathery, sunken patch on the bottom of tomatoes, peppers and zucchini. It looks like rot, but it’s a shortage of calcium in the developing fruit, almost always caused by uneven watering rather than a lack of calcium in the soil. Our alkaline soils have plenty of calcium. Water deeply and regularly, mulch to keep the soil evenly moist, and don’t let pots dry out. Pick off affected fruit; later fruit is usually fine.
Other look-alikes
- Yellow leaves with green veins on young growth of maples, roses, raspberries and others is usually iron chlorosis: the iron is in our alkaline soil but the plant can’t take it up. Compost and organic matter help over time; avoid planting acid-lovers. See soil, compost and watering.
- Twisted, cupped, strap-like leaves on tomatoes, beans, grapes or roses, appearing all at once on several kinds of plants, often point to herbicide drift from a lawn or field treatment nearby. Don’t add anything to “fix” it. Talk to your neighbours, keep the plants watered, and wait; mildly affected plants often grow out of it.
An ounce of prevention
- Build healthy soil. Compost every year. Strong, steadily growing plants shrug off pests that would flatten stressed ones.
- Water deeply and evenly. Drought-stressed plants attract spider mites and flea beetles and get blossom end rot.
- Rotate crops. Move each plant family to a new spot each year so pests and diseases can’t build up. See crop rotation.
- Cover early. Put row covers on the day you plant, not after you see damage.
- Walk the garden often. Five minutes with a coffee each morning catches problems while they’re small.
- Clean up diseased material. Bin (don’t compost) plants with fire blight, black knot or bad mildew. Leave healthy stems and seed heads standing over winter for insects and birds.
- Choose tough plants. Varieties bred for the prairies are less trouble. See trees and shrubs and vegetables that do well here.
Sources
- Government of Alberta, “Dutch elm disease prevention: what you can do” (pruning ban, firewood rules, STOPDED hotline).
- Government of Alberta, “Black knot” (pruning timing and distance, disposal, host list).
- Government of Alberta, “Richardson’s ground squirrel control” (nuisance species status, emergence timing, predators, habitat).
- City of Calgary, “Fire blight” (hosts, symptoms, tool sanitation, disposal).
- Washington State University Extension, “Trap Cropping” (K. Wolfe, 2020).
- Alberta Agriculture and Irrigation, annual grasshopper forecast.
- Environment and Climate Change Canada, severe thunderstorm warning criteria; Canadian Climate Normals 1991–2020, Lethbridge Airport.