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Table of Contents:
This Month's To-Do List | Now Is the Time | Friends of Urban Agriculture
Beating the Bugs | Organic Vegetable Garden
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July To-Do List
- For new plantings, follow instructions on the seed packet and count backwards from the first frost (mid- to late-November) to allow enough time for germination and growth.
- Direct sow additional beans, cucumbers, beets, carrots, corn and summer squash.
- Plant pumpkins and gourds for fall harvest.
- Harvest ripe fruit daily to help keep away unwanted pests, and remove/replace any dead finished vegetable plants.
- Continually harvest warm-weather crops, such as tomatoes, okra, beans, beets, corn, cucumbers, melons and corn.
- Make sure tomato vines have room to grow and are properly supported; trim away yellowed foliage to let in sunlight and remove stems with no flower set that will not grow fruit.
- Harvest garlic, onions and potatoes when tops turn brown and die back; cure root vegetables for a few weeks before storing.
- Visually check plants daily for early signs of pest infestation (such as squash vine borer holes in squash) or for early signs of plant disease (such as mildew on the leaves of cucurbits and melons).
- Keep weeds in check to avoid competition for water and nutrient use by your vegetable crops. Some useful weed identification guides are available from VCE and MGNV.
- Take precautions in your garden to keep mosquito populations in check by removing possible breeding grounds, such as standing stagnant water in gutters, and by encouraging air and light circulation among plants.
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- Stop harvesting asparagus and rhubarb to allow the plants to regenerate and store energy for next year's crop.
- Cover berry bushes and fruit trees with netting to protect your harvest; hanging shiny objects may also help ward off birds.
- Pinch back strawberry runners to allow plants to conserve energy and encourage root growth.
- Plant your sweet potato slips in the garden, mounding up so the roots have room to grow; amply space out the slips to allow the vines to grow and spread.
- Later in the month, plan to start seeds indoors for planting in the fall, such as cabbage, broccoli, Brussels sprouts, cauliflower, collards and kale.
 Plant, Pest, or Other Garden Questions?
Contact the Extension Master Gardener Help Desk. Even during the pandemic, knowledgeable Virginia Cooperative Extension volunteers are available to answer questions!
MGNV July 2021 Events and Classes
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Now is the time to Attract Beneficial Insects while Deterring Harmful Insects and Diseases
 By now you’ve realized that you’re sharing your garden with insects. The good news is that many of these insects are beneficial to your garden. Healthy gardens need and welcome pollinators, parasites (they lay eggs in harmful insects), and predators (they eat harmful bugs). Insects to welcome include bees, butterflies, native lady beetles, spiders, flies, parasitic wasps, lacewings, native praying mantis, and ground beetles. To attract more of these helpful insects, vegetable gardeners often plant nectar-rich flowering plants, such as dill, mustard, sunflowers, Black-eyed Susans, parsley, and goldenrod among their vegetables or nearby.
Consider incorporating certain aromatic flowering plants and herbs to deter and repel garden pests like rodents and mosquitoes, including marigolds, lavender, lemongrass, garlic, garlic chives, rosemary, basil, catnip, bee balm, petunias, and a variety of mints. Consider making plant extracts such as pepper or garlic sprays to spray on melons to help deter these pests. Adding soil amendments, such as blood meal, poultry grit, and eggshells, might also deter slugs and squirrels. Try using rough or sharp materials as deterrents, such as diatomaceous earth, pine needles, or wood chips.
Most gardeners are hesitant to use a pesticide when they’ve spotted insect damage, especially on edible plants. Some broad-spectrum insecticides kill not only unwanted pests, but also pollinators and other beneficial predator insects. Instead of applying pesticides, inspect your garden daily for pests and identify insects to determine whether they are beneficial insects or pests. Check out these resources to help you identify your insect visitor and use cultural controls to minimize pests and disease. Strategies may include picking the offenders off your plants by hand, using a strong blast of water from a hose on the infected area/plant, or pruning away the damaged plant part. Try shaking plants above a bowl of soapy water or spray with a soapy water solution. Be also sure to remove any eggs or larvae left behind. If the problem persists, try some insecticidal sprays that are available at most stores with garden departments.
 Be vigilant for any early signs of common vegetable garden diseases. If you discover, for example, mildew on your basil, cucumber, and squash plants, act quickly: Prune away the diseased bits (throw away, do not compost!); thin out the plant to allow for more air circulation; or remove the plant entirely to avoid spreading to other plants. Consider using disease-resistant varieties of seeds and transplants for your garden or growing alternate varieties (e.g., Thai or lemon basil) that may be less susceptible to disease. Learn more about identifying and managing mildew on basil and cucurbit plants.
Photo: Powdery Mildew on crucife by Scot Nelson
Remember, your Extension Office is ready to help you with your insect and plant disease problems!
In general, reasons why your plants don't thrive may be attributed to not enough sun, crowded conditions, too much or not enough nutrients, poor genetics or maturation, root stress or buds hit by late frost. If your garden doesn't have enough beneficial insects, some fruiting plants might also require help becoming pollinated either with hand pollination or by lightly shaking the plant.
If your garden is struggling because it is not getting enough sun, consider steps to grow plants and cultivate practices geared toward shadier gardens. Some steps you can take include optimizing growing conditions (such as soil preparation, selective pruning, adequate spacing and targeted watering), choosing varieties that yield smaller fruit, growing in movable containers or vertically, using reflective mulch or surfaces or growing in the winter when trees are bare and cast less shade. Check out this list of plants and tips.
Before adding fertilizer to your plants, familiarize yourself with the signs and symptoms of nutrient deficiency and the so-called N-P-K ratio in plant fertilizers: nitrogen (N), phosphorus (P) and potassium (K). For example, a commonly used fish fertilizer for vegetable plants is labeled as 2-4-1 and, therefore, has 2% nitrogen, 4% phosphorous, and 1% potassium. A general rule of thumb for home gardeners is the expression "Up, Down, All Around" meaning nitrogen for green growth (up), phosphorus for root development (down), and potassium for all over health and vigor (all around). Make sure not to over apply these nutrients, especially nitrogen, which can burn roots and kill your plant.
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These recorded VCE/MGNV classes will be of special interest:
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Summer Volunteer Opportunities!
Summer is heating up and so is our need for garden volunteers! Sign up is required for all. When you sign up, please read special safety measures and other requirements for each opportunity.
- Rock Spring Church produce bagging site. The Rock Spring Church produce bagging site receives donated produce and distributes it to local food pantries. It is open on Mondays 1:00pm – 3:00pm in May & July, and Mondays & Thursdays 1:00pm – 3:00pm in August through October. Sign up here.
- TJ Middle School garden. TJ Middle School garden hosts Saturday morning garden work days 9:00am – 11:00am. Sign up here.
- Tuckahoe Elementary School garden. Tuckahoe Elementary School garden has work days Wednesday and Sunday 4:00pm – 7:00pm. Sign up here.
- St. Andrew’s Church garden. St. Andrew’s Episcopal Church “Garden for Hope” is always looking for volunteers. Please sign-up at this link Sign up here.
- Yorktown High School garden. Please email Nate Hankins if you would like to volunteer nate.t.hankins@gmail.com.
- Walter Reed Garden (2040 S Walter Reed Dr). Volunteers work two mornings a week, usually Tuesday and Friday, but we are flexible to respond to weather and harvest schedules. We also need volunteers for one-off projects, which can be scheduled on a weekend. For more information on volunteering, please email Susanna Mcilwaine sumcilwaine@gmail.com.
- Project HUG. The Highlands Urban Garden located in Virginia Highlands Park is looking for volunteers, especially from the nearby neighborhoods. Sign up here.
- Clarendon United Methodist Church. Volunteers typically meet around 8 AM on Saturdays at the corner of Ivy and 6th. Sign up here.
If you would like to sign up for our general volunteer list, click here.
Thank You!
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Illustration © Melissa Joskow
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Pests of Cabbage, Kale, and Collards
The pests of this group of plants are a worthy challenge to our skills as gardeners. There is nothing more disheartening than to see the cloud of little white moths that swarm up from an infestation of whitefly. These plants are also attacked by aphids, cabbage looper, imported cabbage worm, harlequin bug, and flea beetles on an annual basis.
Aphids
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Two spotted aphids and Trichogramma wasp
parasitized aphid mummy in center
(Source: Zack Snipes, ©2014, Clemson Extension)
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Aphids, sometimes called plant lice, are generalists and are pests on many different kinds of vegetable crops. These sap sucking insects come in many different colors, but all will cause disfigurement of the leaf and developing buds, reduce vigor of the plants, and produce excrement—“honeydew”—that may cause sooty mold to grow.
The good news is that they are easy to control and many chemicals are registered for use to kill aphids. Soapy water will knock them down, and there are many beneficial predators that will help you out. Be on the lookout for the aphids that are parasitized by Trichogramma wasps. These aphid mummies host a developing wasp larvae, and if blown up, aphids are present. Take care with your control efforts; you don’t want to remove the helpers from your garden.
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Organic controls include azadirachtin, Beauveria bassiana, hot pepper wax, and insecticidal soaps. Kaolin clay, neem, and pyrethrins will also give good control.
Cabbage Loopers
Cabbage loopers are little, voracious pale green, white striped caterpillars up to 1 ½ inch long that can cause big damage to leaves of all brassica family plants. Larger caterpillars may also eat their way into cabbage heads with the damage looking very similar to that of the cabbage worms.
Several generations of cabbage loopers can occur each year. Handpicking caterpillars off plants and tilling under the soil will help reduce the numbers of active loopers and overwintering pupae.
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Cabbage looper (Trichoplusia ni) (Source: David Cappaert, Bugwood.org)
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Imported Cabbage Worms & Cross-Striped Cabbage Worms
Damage from Imported cabbage worm (Source: Whitney Cranshaw, Colorado State University, Bugwood.org) |
The imported cabbage worm is velvety green with very faint yellow stripes and fine hairs that feeds on the underside of leaves. This familiar white butterfly can be seen in daytime fluttering around cole crop fields. Each forewing has a dark border and one or two round black spots. Eggs are laid singly on the underside or top of leaves, about 1/8 inch in length, light green, and slightly elongated, standing upright.
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The caterpillar, called imported cabbage worm, is gray-green, slightly fuzzy, and sluggish. The chrysalis (pupa) will be green or brown, smooth with three pointed ridges on its back, and attached to a leaf.
Imported cabbage worm adult (Source: Jude Boucher) |
Imported cabbage worm larvae on cabbage (Source: Dan Ferro) |
Cross-Striped Cabbageworm
(Source - Debbie Roos, NC State Extension) |
Cross-striped cabbage worms lay their eggs in batches (3 to 25) rather than singly. Egg batches are yellow, flattened, and attached to the lower leaf surfaces. Larvae grow to 3/4 inch long in 2 to 3 weeks.
The caterpillars are light bluish-gray on top and green underneath, with numerous black bands across their backs and a yellow line down each side. There are 2 to 3 generations per year and are most injurious to late season plantings.
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Organic controls for both imported and cross-striped cabbage worms include the use of biological agents like Bacillus thuringiensis and parasitic wasps (Hyposoter, Copidosoma, and Trichogramma) that can be released to attack these larvae. Organic controls for both cabbage loopers and imported cabbage worm include Beauvaria bassiana, azadirachtin, Bacillus thuriengiensis, kaolin clay, insecticidal soap, neem oil, spinosad, and pyrethins.
Best practices for control also include removal of larvae and pupal cases and thorough end-of-season garden sanitation.
Harlequin Bugs
Harlequin bugs are early pests of brassica plants that overwinter inside plants left in the garden. The colorful, 9.5 mm-long insect goes through six instar stages. It causes significant damage to many kinds of plants by sucking sap from leaves. The injury is similar in appearance to that caused by other stink bugs and by leaf-footed bugs.
Feeding injury by harlequin bug, Murgantia histrionica (Hahn) (Source: James Castner, University of Florida) |
Adult harlequin bug, Murgantia histrionica (Hahn) (Source: James Castner, University of Florida)
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Organic controls include pyrethrins, which can be applied up to day of harvest, as well as several registered chemicals. Cultural controls include removal of garden debris, adjacent weeds, and overwintering crop plants.
Flea Beetles
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Flea beetles on kale,
(Source: Whitney Cranshaw
Colorado State University, Bugwood.org)
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Flea beetles emerge from the soil in early spring to chew holes in the leaves, mate, and lay eggs near the soil line. Its larvae feed on roots and pupate into adults in 2-3 weeks. They will chew many small holes in leaves, and can severely damage young plants.There are multiple generations per year.
Control these with crop rotation, fall tilling of debris into the soil, and using a row cover of floating fabric.Registered chemicals are available for control, but making sure that all plant debris is removed from the garden and the soil plowed or tilled under will reduce the overwintering population. |
Organic controls for serious infestations consist of dusting with diatomaceous earth or rotenone. Azadirachtin, kaolin clay, and pyrethrins are also considered effective in preventing or limiting flea beetle numbers.
Whiteflies
| Whiteflies, in addition to being tomato pests, are also a serious kale and collards pest. Related to scale, leaf hopper, and mealybug insects, adults are only 2 mm long and resemble small white moths. Whiteflies can vector virus diseases, and populations can build up to large numbers very quickly, which will kill plants. Immature pupal cases look like pale yellow-white scale insects on the bottom of leaves. |
Whiteflies with yellow larvae and silvery pupal cases (Source: M.J. Raupp, University of Maryland) |
Next Month: Managing Bird and Mammal Pests
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June Observations from the Organic Vegetable Garden
All photos by Judy Salveson 2021
 In MGNV’s demonstration Organic Vegetable Garden (OVG) in June, the mustard and kale plants exploded into bloom, providing food for pollinators and pleasure for the eyes. By the end of the month, their flowers had faded, and we removed them to our long-term compost enclosure to enrich next season’s crops. We will plant more mustard, kale, and other winter brassicas later in the season, after the whiteflies, aphids, and cabbage worms of summer have subsided.
The biggest effort in June was directed at planting small and large fruited tomatoes, sweet and hot peppers, eggplants, and beans of many varieties. We will continue to provide support for these growing crops through harvest.
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Our harvest in June included the garlic planted last November and green onions planted this spring. We were dismayed to find that the allium leafminer had made homes for their growing larvae in both these allium crops. Nevertheless, we were able to rescue most of the crops by harvesting before major damage was done to the bulbs. We removed stems and greens containing larvae to the trash, to prevent them from occupying the rest of our crop or our compost.
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On the other hand, we were delighted by our harvest of an unexpected bumper crop of spring turnips, apparently encouraged by soil enriched by cover crops, compost, and a generous amount of rain.
Stop by and visit the Organic Vegetable Garden at Potomac Overlook Park
2845 North Marcey Road, Arlington, VA 22207
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For more information on Vegetable Gardening, check out Select On-Line References for Kitchen Gardening on the Master Gardener of Northern Virginia (MGNV) site. MGNV volunteers support the work of Virginia Cooperative Extension's public education outreach.
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