Common Garden Pests & Diseases Part 2
Pests and diseases in the garden are pretty much inevitable. Here at Territorial, there are some common issues we see each year, so we will be posting a series of blogs to discuss best practice for handling these topics. This is not intended to be all-encompassing, and you may find another management practice that works better for you.
Aphids
Almost every gardener has likely dealt with this pest at one time or another. While they are typically more of a nuisance than deadly, their feeding can weaken a plant, making it more susceptible to other pathogens and pests, and can spread disease.
Identification
Aphids are small, pear-shaped insects that come in a variety of colors, ranging from yellow/green to red, brown, and black. They are typically 1/32 to 1/8 inch and may or may not have wings. Aphids are also typically found in groups and leave behind a residue called honeydew, which can be used to identify them.
Life Cycle
Eggs overwinter on woody stems. Stem females hatch in the spring, giving birth continuously throughout the season to live nymphs – mating is not required. Nymphs take 1-2 weeks to mature and look similar to adults. Males and regular females are born in the fall, then mate to produce overwintered eggs.
Host Plants
Aphids can be found on a wide range of plants including small fruits, vegetables, ornamentals, as well as fruit and shade trees. Some species of aphids will feed on cereal crops for part of the year before moving on to fruit trees. In the garden, aphids are commonly found on cucurbits, brassicas, nightshades, legumes, flowers, stone fruit, carrots, spinach, lettuce, fruit trees, and milkweed.
Impact
Both nymphs and adults suck plant sap, which can cause yellow leaves and stunted growth as well as leaf, bud, and flower distortions. Misshapen and stunted fruit forms on infested branches, and heavily infested leaves and flowers will drop off the plant. Feeding can also spread viral diseases. In fact, aphids are the primary group of virus carriers (vectors). Aphids have piercing, sucking mouthparts that include a needle-like stylet, which allows aphids to access and feed on plant cells. When feeding, aphids ingest sap while also injecting saliva. This saliva can contain viruses if the aphid has already fed on an infected plant.
Aphids can spread viruses through two categories of transmission: non-persistent and persistent/circulative. In non-persistent transmission, viruses can be both acquired and spread in a very short amount of time – less than one minute – although the viruses stay viable on the aphid’s mouthparts for only a few hours. After the virus loses its viability, the aphid must feed on an infected plant again before it can infect more plants. With persistent transmission, it takes the aphid substantially longer – several hours – to obtain the virus, and it takes approximately 12 hours for the virus to circulate through the aphid’s body and become transmissible by the salivary glands, although once this occurs, it remains transmissible for several weeks, if not the rest of the aphid’s life.
Management and Control
There are several options for reducing the likelihood of aphids in the garden.
Keeping your garden tidy and free of debris and weeds will reduce the areas where aphids may harbor.
You should always check transplants, especially from outside sources (garden centers, nurseries, etc.) before introducing them to your garden, removing any aphids you find.
The use of protective covers when starting seeds outside can help protect them from most pests, as can starting seeds indoors and waiting to transplant them until they are more mature.
Planning your garden to include plants that will attract native predators, such as lady beetles and lacewings, can help keep aphid numbers lower and may prevent the need to treat.
If possible, using reflective mulch in the garden can also help reduce the number of aphids, as well as a wide range of other pests.
One of the most important actions you can take is regularly checking your garden for aphids and removing any you find as soon as possible. This can be done by hosing them off or pruning off heavily infected areas. One giveaway that you may be dealing with aphids is large numbers of ants crawling on your plants – this is typically a sign that honeydew is present, and aphids (or another pest) are nearby. It’s important to note that aphids do not typically kill mature plants, so treatment is not always necessary and can have an impact on beneficials that utilize the plants as a food source as well.
It is recommended to only treat when substantial damage is occurring or when the infestation is beyond the point of being managed by pruning the plants or spraying. If you do decide to treat, you can use Neem, insecticidal soap, or horticultural spray. Only use commercial spray as an absolute last resort.
Leafminers
Leafminers are common garden pests that leave distinctive tunnels in leaves. Leafminers are broken into two categories – flies and sawflies – with similar features and impact.
Identification
Flies: Leafminer fly eggs are white and cylindrical, found in clusters on the underside of leaves. Larvae are translucent pale green, about 1/8” and stubby, typically found in the tunnels they make. Adults are black or black-yellow, about 1/10”, and rarely seen.
Sawflies: Sawfly larvae are flattened, white maggots with brown heads and no legs. Adults are about 1/5” and stout. They are black with transparent wings.
Life Cycle
Flies: Adult leafminers overwinter in cocoons, emerging in early spring. Eggs are laid on the underside of leaves. Larvae mine leaves for 1-3 weeks, after which they pupate in soil for 2-4 weeks. There are typically 2-3 generations per season.
Sawflies: Sawfly larvae overwinter in cocoons in the soil, where they pupate. Adults emerge in mid-May and lay eggs on leaves. Larvae feed in leaves until they are ready to pupate. There are up to four generations per year.
Host Plants
Flies: Leafminer flies feed on a wide range of vegetable plants, including members of the Solanaceae, Apiaceae (celery), Cucurbitaceae, and Amaranthaceae (spinach, chard, beets) families as well as legumes, onions, and lettuce. They will also feed on ornamentals such as holly and columbine.
Sawflies: Leafminer sawflies feed primarily on the leaves of elm, birch, and alder trees.
Impact
Flies: As their name suggests, fly larvae tunnel within the leaves of the host plant, feeding on leaf tissue and leaving behind round, winding, hollow mines. The damage caused by this mining can destroy seedlings, although on larger plants, the damage is more of a nuisance and an eyesore.
Sawflies: Sawfly larvae cause similar damage on tree leaves, although with this damage comes browning leaves and wrinkled blisters or blotches in leaves. Damaged trees are weakened and are more susceptible to borers and other pests.
Management and Control
The most important management tool is frequent monitoring (especially of first true leaves), removing and destroying damaged leaves and egg clusters as you find them.
Of course, general garden cleanliness is equally important. Control weed populations and remove debris regularly. Once your harvest season is complete, remove plants and till your garden.
A physical barrier such as a fine mesh can keep leafminers off your plants.
If possible, include plants that will attract native parasitic wasps.
Do your best to keep your plants healthy and vigorous.
Treatment is typically not required for vegetable leafminers, although Spinosad can be used if necessary.
Powdery Mildew
Powdery mildew is a wildly common garden issue with an incredibly wide range of hosts due to the many fungi that cause it. It is relatively distinct, although may be confused with downy mildew on some plants.
Identification
Powdery mildew is typically first seen as yellow leaf spots that eventually produce white powdery spots or mats on both sides of the leaves. Watch for fruit that is ripening when smaller than anticipated and leaves that look like they’ve been dusted with flour.
Host Plants
Each species of fungi has its own set of hosts, and the list of plants that can be impacted is vast. Powdery mildew is often found on cucurbits; fruit plants such as blueberry, apple, and grape; and a wide range of flowering plants such as phlox, snapdragon, and zinnia.
Impact
While powdery mildew is commonly more of an eyesore than anything, especially on flowering plants, infected fruit can be impacted. Fruit of an infected plant may crack or have raised webbing, called russeting, on the surface. The fruit may stop changing color or change slowly. Plants will usually produce fewer and smaller fruits than expected, and fruit may ripen prematurely. The fungi mostly attack new leaves, which will cause distorted growth and could impact productivity.
Management and Control
Unlike many fungal infections, powdery mildew thrives in hot weather, especially when the nights are cool, and, unlike most fungal infections, is typically less of a problem in rainy weather.
As with most garden issues, monitoring for infection is one of the most important steps you can take, especially during periods of heat or drought.
Proper garden management plays a key role in preventing infection. Make sure to provide proper airflow through spacing, staking, and weed control.
Keep your plants healthy and happy by maintaining proper moisture levels and ensuring the plants receive the right amount of sunlight. Drought-stressed plants are more susceptible, so consider using mulch to reduce stress and maintain moisture levels. Water from the base of the plant, rather than above, to help prevent spores that may be present in the soil from splashing onto the plants.
Have a soil test done before applying fertilizer and avoid applying too much nitrogen.
Varieties with partial resistance may be available, so consider planting those, especially if you’ve struggled with powdery mildew before.
If you do find powdery mildew in your garden, remove infected leaves as soon as possible, washing your hands and sanitizing your tools before moving on to other plants. The infected plant may be left to finish out the season, at your discretion, since nearby plants may already be infected. Removed plant material can be composted, as long as proper composting techniques are observed.
You can also treat your garden for powdery mildew. Several organic sprays are available for persistent infections. These sprays can provide control and limit the spread. You can also make a treatment at home using a .5% solution of baking soda (1 teaspoon for a quart of water). If the infection is overwhelming, you can use horticultural oil products including Neem oil, fungicidal soap, and sulfur or lime-sulfur sprays as a last resort. Bacillus subtilis and potassium bicarbonate can be used as well. When you spray infected plants, be sure to do so thoroughly, following the directions on the bottle, and continue monitoring the infection.
Stay tuned for more! And as always, if you have any questions regarding these or other garden issues, our team is always ready and eager to offer support!
Author: Ashley W.
