Mary's Veggie Garden

May 14, 2017

Protecting the Harvest with a Row Cover: part 1, Why a row cover?

A row cover is a non-woven fabric covering used in vegetable gardens to protect plants. Row covers come in different weights for different purposes. The lightest covers pass the most sunlight and are used as an insect barrier. Heavier row covers protect plants against frost but pass less light.

In this post I will discuss the lightest weight floating row cover which is used to exclude insects from the vegetable plants and the specific pests I protect against in my garden. My next post will cover how and when to install a floating row cover in the garden and how big a row cover is needed.

A floating row cover protects potatoes against successive pests in my garden: in May flea beetles, in June Colorado Potato beetles, in July potato leaf hoppers.

Some Motivation

Have flea beetles ever killed eggplant transplants in your garden? Flea beetles are tiny, black insects. They jump when disturbed so you may never  see one, but you might recognize the damage they leave behind. Flea beetles prefer to feed on hairy leaves in which they chew tiny holes. In my garden I use a floating row cover to protect Chinese (Napa) cabbage from flea beetles.

Flea beetles and their feeding damage on Chinese cabbage. (Greatly enlarged to show insects.)

Growing kale and other cabbage family crops has gotten more and more challenging. First there were imported cabbage worms.  I remember the first time I cooked my own broccoli and discovered that imported cabbage worms turn grey when cooked. Yuck! About 4 years ago I saw the first cross-striped cabbage worms which are even more devastating. The adult moth lays her eggs in clusters of 20 or so and when the caterpillars hatch and start feeding they quickly turn a kale plant into lace and frass.

Cross striped cabbage worms devastating my kale.

Imported cabbage worm on cabbage.

Do squash borers kill your zucchini every year just as the harvest starts? The adult borer is a moth who lays her eggs on the stem of zucchini & summer squashes starting about the time the chicory blooms and finishing up by the end of June in Dutchess County, NY. It is safe to remove row covers from squash plants on July 4. Squashes are pollinated by bees and must be uncovered for pollination.

Mexican bean beetles are a plague in the community gardens. Many gardeners mistakenly protect these voracious pests because of their close resemblance to their ladybug cousins. Although shape and size are identical, bean beetles are  orangey-brown or copper while ladybugs are red. Bean beetle larvae are bright yellow and feed on the underside of leaves. A row cover provides effective protection for bush beans. Most beans are self-pollinating so the row cover can be left on the plants through harvest. I’ve covered edamame soy beans and bush beans grown for drying.

Mexican bean beetle adults and larvae.

A Floating Row Cover

In my garden I’ve been using Agribon AG-15 Insect Barrier. It is 118″ wide. Here is the description from http://www.johnnyseeds.com.

Lightweight grade for insect control.

Also for heat-sensitive crops – only a minimal heat increase during the day. … Effective control of insect pests on potatoes, greens, cabbages, and radishes. 90% light transmission. 0.45 oz/sq.yd.

What does this mean? Light weight – the row cover doesn’t need support. It is light enough to be supported by most plants as they grow. It is also light enough that heat does not build up under the row cover. I’ve kept my broccoli covered all summer, uncovering only briefly to harvest.

90% of the sunlight reaches the plants under the row cover. In full sun plants don’t notice any difference in sunlight. I’ve covered zucchini squash in my part-sun home garden. The plants might have preferred a bit more light in their youth, however they lived through a full season because of the early summer protection from squash borers.

Water easily passes through the AG-15 row cover. Rain reaches the planting through the row cover.

Alternatives

Alternatives to a floating row cover include hand-picking the insects off the plants and spraying various insecticides. It is easy to hand-pick cabbage worms from kohlrabi because the leaves are flat and the crown of the plant is open and easy to inspect. In contrast, it is almost impossible to find cabbage worms feeding in a head of broccoli so I always row cover my broccoli.  The insecticide Bacillus thuringiensis is rated for organic gardens and is very effective against cabbage worms but it must be sprayed every 7 to 10 days to protect new growth.  Can you maintain a regular spray schedule? It is a challenge.

Flea beetles are  very jumpy, impossible to see and hand-pick. Squash borer eggs are laid on the stiff main vine of the plant which is quite stiff and difficult to inspect for eggs. Once the borers hatch, they chew their way into the stem which keeps them well hidden.

Because I’m a lazy gardener, I choose to protect some crops plants with a floating row cover rather than spray or hand-pick.

In my next post I will explain when and how to install a floating row cover in your vegetable garden.

September 11, 2012

Edamame Harvest Disaster

Filed under: Beans,Edamame,Gardening,Insects,Mexican Bean Beetle,Pests,Stink Bugs,Vegetables — marysveggiegarden @ 7:44 am

Usually the soy bean harvest is a time of contentment and of rewarding, hard work. This year it is devastating.

The harvest process goes like this: Click here for a look at last year’s harvest.

  • Lop off the bushy plants at their base.
  • Snip off the lush, green foliage to reveal the branching stems crowded with pods. Return the foliage to the garden as mulch.
  • Pull off the pods, each bulging with 2-3 full-sized beans.
  • Fill a couple of plastic grocery bags with pods for the bicycle trip home from the community garden.
  • Steam the pods for 6-7 minutes, then cool quickly in cold water, then shell.
  • Repeat for 4 days, until the harvest is finished.

The family shelling party is a chance to chat, as we fill bowls with the perfect,bright green edamame beans.

The story is very different this year. (Click on any picture to enlarge.)

There is no lush green foliage. Most of the leaves are completely skeletonized by Mexican bean beetles. The few remaining green leaves have several bean beetle larvae feeding or metamorphosing on the their undersides.

Mexican bean beetle larvae on edamame soy. The larvae with white noses are the older ones, metamorphosing into adults.

Mexican bean beetles prefer common green beans and their close relatives (Phaseolus vulgaris) but if they can’t get green beans they will switch to soy (Glycine max). After killing all the green bean plants in the area the beetles attacked my soy at mid-summer when the plants were big and bushy.

Soy plants with whole branches of flat pods and leaves skeletonized & killed by Mexican bean beetles.

As usual, pods crowd the edamame stems. But this year about a third of them are flat, with only the merest hint of a bean inside. Another third contain small, very underdeveloped beans. And a third have full-sized beans. I attribute the flat pods and tiny beans to defoliation – it is difficult to grow full-sized fruit with almost no leaves. I’ve been growing edamame soy at the Vassar Farm community gardens since 2005 and this is first time I’ve lost a crop to bean beetles.

So I filled a single bag with full and undersized pods. It was very light-weight.

2012 Soy harvest

Last night I steamed the pods then we shelled out the beans. Instead of perfect green beans, they have brown spots and sunken areas. About half of the full-sized beans are damaged along with 90% of the underdeveloped beans.  And some of the beans in the OK pile have suspicious tan areas I don’t recall ever seeing before. The pods themselves look fine, with no hint of the damage waiting inside.

Stink bug feeding damage on edamame soy beans.

I’m attributing this damage to stink bugs. They seem to have these micro-fine stiletto mouth parts they can insert into fruits and vegetables (apples, tomatoes, peppers) without visible damage to the skin. During harvest I’ve found  both green stink bugs and brown marmorated stink-bugs, both nymphs and adults. I’ve squashed more than a dozen. (It took 5 minutes to collect the bugs in this picture from an asparagus planting in a local public garden. Photography took considerably longer, the things won’t stand still.)

Green stink bugs and brown marmorated stink bugs, both nymphs and adults.

I read some research from Ohio State University. Stink bugs feed by injecting saliva into the fruit, then sucking out the pre-digested contents. The digestive enzymes stop development of the fruit, leaving corky areas. So it is possible the stink-bugs have caused a lot of the under-developed beans. Although it is possible to cut stink bug damage out of a tomato, the damage fills most of a soybean so I’m discarding damaged beans.

Now, after harvesting three-quarters of the soy bean patch, yield is about 20% of normal.

Our conversation while shelling the beans got rather dismal. The brown marmorated stink bugs are invasive. In the last few years they’ve spread rapidly up the east coast. And according to Rutgers there are no good controls. On our trip across NYS last week we passed hundreds of acres of soy beans and apples, two crops by brown marmorated stink bugs. And there is drought through-out the grain belt. Is the time coming when the US will be unable to feed itself, never mind feeding Africa?

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