September/October – Fall and Winter Pests

Beating the Bugs

Tomato Hornworm illustration — Illustration ©
Melissa Joskow

The information here was originally published in a monthly column on pest control in Between the Rows – A Guide to Vegetable Gardening published by VCE in collaboration with MGNV.

Don’t miss Kirsten’s in depth online class:
What’s Eating My [Cucumbers, Tomatoes, Eggplant, Beans, Squash]? :
Insect Pest Management for the Vegetable Garden

Fall Crop Pests and Tips and Tricks for Reducing Overwintering Pests

I am often asked to diagnose plant disease and identify pest problems and other types of troubleshooting for school and community gardens. The challenges of maintaining school gardens over a long hot summer that are only used for teaching or after school classes have led many to planting a quick spring garden and a fall garden plus a thick nitrogen-supplying summer cover crop of clover or buckwheat in between. No need to water long season crops like tomatoes and corn or peppers over the summer, no need to worry about weeds, and no need to have to deal with all the plant diseases and pest insects that feed in our gardens over the hot summer months.

As fall approaches, the pressure to manage garden insect pests is off! Many of the most common insect pests have completed their life cycles and will move into the soil to pupate or have laid their eggs before dying in hopes of a new generation the following year. This means that we can clean up the messy summer garden, throw away the squash vine borer-eaten vines, and replant a fresh fall crop of greens that will take us into December and beyond with a little protection.

There is much that we can do to interrupt the life cycles of overwintering crop pests and reduce the occurrence of pests in next year’s garden.

Mexican bean beetle (Epilachna varivestis) multiple life stages — Mexican bean beetle life cycle stages, clockwise from the right: larvae eggs, eggs, adult eggs, and pupae. (Picture courtesy of Clemson University – USDA Cooperative Extension Slide Series).

1. Sanitation

Remove all spent growth of plants that are no longer bearing or have died back. Remove tall weeds both in and around the garden too. This will remove eggs that have been laid on or inside of stems or that will fall to the ground and be protected by the dead foliage of your garden plants. The Mexican bean beetle, for example, is one pest that will re-infest your garden in this way; it can be controlled with garden cleanup and removal of dead foliage. Rake up diseased leaves and stems and dispose of in trash NOT compost piles. Unless your compost pile is hot enough to kill these pathogens, they will live on in the compost and provide a source of disease inoculants next year.

2. Tilling the garden

There is debate about the value of this practice and different ideas about how to do it. My advice is that turning over the soil by whatever means available is a valuable way to disrupt the life cycles of insects that pupate or overwinter in the soil as adults. Grubs and cabbage loopers are two garden pests that can be reduced by turning the soil. This can be done in late winter as preparation for spring planting. It can also be done in the fall. If you have used woodchips for pathways, the fall is a great time to add that final layer of chopped leaves and lawn clippings and mix it up with the partially decayed wood chips to distribute organic matter into the root zone of the plants and to aerate the soil. Keep in mind that you will want to add supplemental sources of nitrogen to your garden to not only provide a nutrient source to your spring crops, but also to help break down these carbon rich materials. Here is some more information about Carbon to Nitrogen Ratios.

3. Rethinking our crop selection

All of us should keep notes on our gardens to keep track of varieties that performed well, what we liked to eat, what the weather did, how the plants performed against pests. It is also helpful to look back and find dates of pest emergence so that we can be on the lookout for them in future gardening years. Consider conducting a survey of your garden community to compile this list of varieties that did well for others and sharing it. Here is a list of plants and vegetable crops with known disease and pest resistance.

4. Work on your compost piles

Work on your compost piles. A home source of good compost is worth the time it takes to create it. Building a bin to contain it is a good way to help make it less unattractive and to get a critical mass. To achieve the heat needed to kill off undesirable pathogens and insect eggs, it will need to be at least 4x4x4 feet in size. Fall and winter leaf pickup and the addition of kitchen scraps provide ample material and moisture to provide at least partially decomposed materials by spring. Another way is to compost in place by building a temporary – or permanent – fence around your garden beds for the winter and simply piling up layers of green (wetter, fresher materials) and brown (leaves, shredded paper) inside that area. Arborist wood chips can be laid down in paths and trenches to add additional food for microorganisms that will help break down your organic matter.

For more ideas on soil building and composting, go to these classes in our Public Education Virtual Classroom:

5. Plant and prepare the fall garden for overwintering

Low row cover using plastic sheeting and PVC at the Fairlington Small Space Garden.
*(Photo Kirsten Conrad 2020)*

Because we gradually lose hours of sunlight in the fall and winter months, the crops that we can grow successfully here in the winter are those that we harvest the leaves from. Crops that produce from flowers will need a minimum of 6-8 hours of sunlight a day. An added bonus is that many of these cool season crops are capable of overwintering with a small amount of protection. Kale, cabbage, collards, and some root crops like carrots and radishes when planted no later than September can produce well into the winter. Some like it cold — arugula, lettuce, and cilantro won’t tolerate freezing temperatures, but will grow abundantly in the fall.

Simply throwing a cover over your in-ground crops can provide 4-6 degrees F. of protection from frost. Adding a low tunnel hoop type of row cover that will trap the sun’s heat can help use the soil’s ability to store and release solar energy. Using the cold winter months to construct a cold frame from recycled windows will give you a mini greenhouse to start spring seeds in. Here are instructions: DIY Cold Frame Plans. No, you won’t be able to grow tomatoes or other heat loving crops without supplemental heating, but there are plenty of crops that you can not only grow but also harvest through the winter months if you provide protection. And the good news is that there are very few disease or insect pests that will bother your cold frame/low tunnel overwintered vegetable crops.