Cooperative Extension Publications

Controlling Insects and Other Pests Organically

Controlling insects is important. Row covers are essential to keep insects such as flea beetles (which love all brassicas—kale, cabbage, broccoli, etc.) from putting shot holes in the leaves of your plants. Row covers come in a variety of lengths, weights, and widths. For garden beds our size, I like to buy “15 weight” (for insect control) floating row cover. It comes in 250-foot rolls and is 118 inches wide. The key to effective row cover management is to roll out your cover the length of the bed plus a couple of extra feet on each end. So, for a 4×10 ft bed, I might roll out 14 feet of row cover to make sure there was enough material to cover the plants and not blow off. I measure the length of row cover required by counting the number of foot falls heal to toe walking down the alley next to the bed in question, and then I add two more feet for each end to have plenty of extra material to bury and hold down with rocks. If you have a carpenter who might be replacing old windows, ask him/her to save you the anchor weights. They make excellent weights to ensure the fabric stays in place. The other key component is to try to bury the edges of the row cover to prevent the wind from blowing the cover off.

When storms or heavy winds are expected, it is worthwhile to go out to the garden and check the status of the row covers. It’s a good time to tuck in corners and check weights or sandbags holding down the row cover. It is also good to check after the storm is over. Sandbags can also be purchased or made to hold down row covers.

It is essential to cover the beds immediately after you sow or transplant. Flea beetles are small black insects that are barely visible, and they can do great damage to newly emerging leafy greens or transplants. It is also essential to thoroughly water your transplants and your newly seeded beds prior to covering. Although row cover fabric is designed to allow water to penetrate, a good percentage will run off. So, making sure everything is well watered prior to covering it with row covers is essential. The cover warms the soil on cool nights, keeps the wind from whipping your new transplants, and keeps vertebrate animals from dining on your handiwork, which can also be beneficial. Row cover has not traditionally been needed for some leafy greens, such as Swiss chard and spinach, unless leaf miner insects are active in the area. They can eat the epidermis of the leaf, leaving unsightly patchy areas on the leaf. That is why they are said to mine out the leaf. As well, we never really needed to cover onions or other allium plants. However, you should be aware of thrips and the leek moth, which is becoming increasingly damaging in Maine and the Northeast U.S. I hope we don’t end up having to cover everything in a garden, as it is not particularly attractive to cover everything.

Beautifying Your Garden to Attract Beneficial Insects

You can plant flowers in front of your production garden to make the area more attractive. Flowers such as borage attract beneficial insects to the garden. Other flowers, such as marigolds, are thought to keep away insect pests. You can plant flowers in the front of a bed and tuck the row covers behind them. Scarlet runner beans, shown here, are also beautiful and provide a lovely backdrop to the garden.

Slugs can be a very problematic production pest. Slugs crawl or burrow under the row cover and will feed on leaves and burrow into cabbage heads. It is not fun to have slugs in the cabbage heads that you want to deliver. There is an organically approved product called Sluggo that serves as a repellent to slugs. The product consists of pellets of iron phosphate, which the slugs don’t care for. You should put it down when you transplant cabbage seedlings, and reapply as often as you pull off the covers to weed. Always recover your plants until they have grown so large that they might not fit under it. We typically apply Sluggo four times a year. Although it is relatively low risk, make sure to read and follow all label instructions, as it is a registered organic pesticide product.

There are other organic products that can be used in gardens if insect pressure is high enough. Through effective crop rotation (discussed in the vegetable-specific sections of this guide; also see Crop Rotation for Home Gardeners), you may be able to prevent too much insect pressure and will not have to resort to other organic insecticides like PyGanic or other pyrethrum products. We have used only iron phosphate repellents in our Orono Community Garden.

Finally, when you are working the soil, look closely for insects. Earthworms are always good things. But in turning over the soil you will often find larvae, pupae, and adults of insect pests. Wireworms commonly overwinter in soils; they are small 0.5-inch tan, hard wormlike organisms. It’s generally a good idea to remove these from your beds if you locate them.

Controlling Fungal Pathogens in the Garden

We have generally not had major issues with fungal organisms in our gardens. We use bed rotation to prevent pathogen buildup in soil. Also, some cover crops such as mustard can be useful to suppress these soil-borne organisms. There is somewhat less control over airborne fungal pathogens. Some people apply copper-based fungicides, but again, I don’t like to use even organic pesticides if it’s not necessary. It is important to carefully monitor the plants for any symptoms. Take advantage of the Cooperative Extension resources that are available. In Maine we have experts who will identify specific pest and diseases that might afflict your garden. There are also fact sheets describing specific insect pests and disease symptoms. Taking advantage of these resources may help you avoid more serious issues. Early and late blights of tomato can be and have been a problem at various times, and you should be familiar with the symptoms of each of these diseases.

Controlling Weeds in the Garden

Weeds are easy to control in a reasonably sized organic garden. There are three real keys to effectively controlling weeds:

• weed early and often with the right tool for the job
• don’t let weeds go to seed
• be ready for the annual grass flush in July and August that can take you by surprise.

Traditional hoes are not very useful, particularly for early garden weeding. I like small specialized hoes like loop hoes and other special tools to be able to carefully weed close to new transplants such as onions. Loop hoes are circular and are designed to disrupt germinating weed seeds early in their growth stages (in what many refer to as the thread stage of growth) without disrupting too much soil. They can cut the germinating weeds before they emerge. Traditional hoes are useful to weed in the alleys, but not so much in the production area.

I can handle a few “imposters” in the garden, and early in their growth some weeds (e.g., lambsquarters and purslane) are quite edible. But if plants are allowed to go to seed, problems intensify each year. As the garden season progresses and the days start to shorten, weeds will go to seed at a much smaller size. So, keeping at the weeding and not letting plants go to seed is important. One important thing to do in beds like onions and other alliums is to weed before you think you need to. You will be disrupting germinating weeds when you carefully weed around transplants before you see weeds emerging.

Mulching alleys with barley straw or other materials is a very good means of controlling unsightly weeds. Sometimes the row covers can shade out emerging weeds, but if not, then barley straw makes a nice weed discouraging cover. Scratch the soil to ensure that you have disrupted any germinating weeds, then spread 3–4 inches deep of straw in the alleys after the beds have been sown.

Lastly, the flush of annual grass in late July and August can be a real headache. You think you have managed your weeds, and then there is often a flush of growth. Both annual and perennial grasses such as quackgrass always require time and effort to control. Quackgrass reproduces with underground rhizomes, which need to be dug out intact and disposed of. Annual grasses should not be allowed to go to seed. Weeding should be approached as a Zen-like activity. But if you start to hurt, back off and rest. Gardening should not inflict pain!

Controlling Vertebrate Pests in the Garden

We have had moderately good luck through the years with vertebrate pests. The biggest issues we typically have are deer, groundhogs, and cats. Early in the season, with many beds covered with row covers, we don’t have a lot of issues with deer. It is generally later in the year that we begin to have issues. Deer love Swiss chard and beets. So, if your area is loaded with deer, you should expect some feeding damage. Groundhogs are tricky too. Our garden has tremendous groundhog habitat, because a train track runs below the garden, and groundhogs burrow into the side of the hill. We have trapped them with live animal traps, but they are a bit wily, and you might catch a skunk if you are not careful. Unfortunately, cats sometimes like to use raised beds as their litter boxes. I find it frustrating, and I have yet to figure out what to do about that. Finally, we have had snapping turtles come and burrow in the soft beds to lay their eggs. Tell me what to do about that? They can be run out of the garden, but they will return. Fencing would be a solution to all these issues, but our garden is shaped so that this is impossible. So, we tend to rely on close inspection/monitoring and a lot of hope.

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