In the Garden Cabbages & Cabbageworms

April is halfway through and avid gardeners are tending cool-season crops including cabbage, broccoli and cauliflower. Cabbages are a favorite garden crop because they are simple to plant and quick to grow. They are a wonderful food for humans — and cabbageworms.

The three most prevalent cabbageworms are imported cabbageworms, cabbage loopers and diamondback moth larvae. While all three occur in Kansas, imported cabbageworms and cabbage loopers are the most common. And because they are the largest, they are the most destructive.

|Imported cabbageworms have a green velvety appearance and sometimes called green fuzzies. Cabbage loopers, which are green and hairless, are referred to as inchworms because of their looping/inching movements. The parents of imported cabbageworms and cabbage loopers are butterflies and moths, respectively. Most people are familiar with imported cabbageworm butterflies because they fly during the day. Few are familiar with cabbage looper moths because they fly in the dark of evening and early morning hours.

Overwintering as chrysalids, imported cabbageworm butterflies may appear during brief warm spells in February, but typically do not begin activities until mid-March. Cabbage loopers also overwinter in the pupal stage encased in flimsy, silken cocoons. Both survive winter protected beneath debris and litter.

These two pests differ in larvae appearance and life stages from larva to adult. Both imported cabbageworm butterflies and cabbage looper moths flit about and glue individual eggs to plant hosts. Imported cabbageworm eggs are primarily deposited on lower leaf surfaces, while cabbage loopers prefer to lay eggs on top. Imported cabbage worm eggs are yellow and somewhat elongated. Cabbage loopers eggs are white and more rounded.

Both species produce more than a single generation per year. Although not specifically documented for Kansas, the literature mentions that imported cabbageworms produce between three and six generations per year with cabbage loopers producing three to four. In this newsletter we are addressing the impact of both species on cool season crops (spring and fall), but they are present throughout the summer, sustaining their populations on alternate hosts of plants and weeds as well as cultivated crops.

Beyond these differences, both cause similar damage. Direct feeding damage and fecal deposits render cabbage heads unmarketable. But washing away worms and fecal pellets may salvage them. The remaining head is safe and edible.

Vigilant gardeners can prevent severe damage by looking for the presence of white wings, the first hint of potential problems. When butterflies light, observe egg laying by examining that leaf for the presence of a newly deposited eggs. Holes appearing on the outer wrapper leaves indicate the presence of cabbageworms and the need to reduce populations before they begin moving to the developing head.

Numerous insecticidal products are registered for use against vegetable pests such as cabbageworms. They are rated both as nonorganic (synthetic insecticides) and organic (botanicals, spinosyns, bacillus thuringiensis, horticultural oils, horticultural soaps) products. Check local retail outlets for availability.

What is that Buzzing? It is March Flies!

Have you been seeing fairly large midge-like insects flying around people and crabapples (Malus spp.) in full-bloom? These are adult March Flies (Family: Bibionidae), and most are in the genera Bibio or Dilophus. One common morphological characteristic for identification is the presence, on the wings, of a very distinct yellow-brown stigma (spot) among the veins. March flies are in the same family and are closely related to love bugs. Female March flies dig holes in the soil in which they deposit approximately 200 to 300 eggs in a mass. They die soon after laying eggs. Eggs hatch into larvae that are yellow in color with dark spiracles and a shiny brown head. Larvae live in moist habitats and feed on decaying organic matter and among plant roots. They may enter potatoes that are damaged by insects such as wireworms (click beetle larvae) or diseases. Adults are most active in spring and summer, and may be present in abundant numbers (as people have experienced). They are attracted to flowers and may be important pollinators, but they are also attracted to homes and people.

Preventing the Spread of Pine Wilt

Pine sawyer beetles, Monochamus caroliensis, which emerge from dead trees and transport the pinewood nematode to healthy trees, perpetuate the pine wilt disease cycle. Trees killed by pine wilt disease are reservoirs for pinewood nematodes. The larvae of pine sawyer beetles overwinter as mature borer larvae. Currently, they are preparing to pupate within their pupal chambers. After a beetle emerges from its pupa, it remains in the pupal chamber briefly while its exoskeleton hardens. Pupae and beetles are inactive — an ideal time for dispersal-stage pinewood nematode larvae to invade the transport host.

To prevent this, destroy diseased trees by burning them by mid-May. Beetles begin to emerge in April and continue for about a month. Timely burning means destroying trees before current season beetles emerge. It is best to burn early, preferably by April 1 to get this chore out of the way. With the weather warming-up, other pressing needs may delay burning until beetles have emerged and it is too late. Do not neglect this yearly chore, especially in pine wilt disease-free areas of the state.

Setting Out Tomatoes

Gardeners often try to get a jump on the season by planting tomatoes as early as possible. Though this can be successful, there are certain precautions that should be observed.

Harden off plants: Plants moved directly from a warm, moist greenhouse to the more exposed and cooler conditions outside may undergo transplant shock. Transplant shock causes plants to stop growing for a time. Plants can be acclimated to outside conditions by placing them outdoors in a location protected from wind and full sunlight for a few days before transplanting. Another way to harden off plants is to transplant them and place a cardboard tent or wooden shingle to protect them from wind and sun for 2 to 3 days. The best conditions for transplanting is an overcast, still day.

Protection from frost: Tomatoes cannot tolerate frost. Though we are past the average date of the last frost in most of Missouri and Kansas, watch the weather and cover the plants if frost threatens. A floating row cover or light sheets can be used for protection. Actually a floating row cover can be left on the plants for two to three weeks to increase the rate of growth and establishment.

Adequate soil temperature: Tomato roots do not do well until soil temperatures reach a fairly consistent 55 degrees F. Check the temperature at 2 inches deep during the late morning to get a good average temperature for the day. Plastic mulch can be used to warm soil more quickly than bare ground. Purple leaves are a sign of phosphorus deficiency due to too cool soils.

Other tips for getting tomato plants off to a fast start include:

1. Use small, stocky, dark green plants rather than tall, spindly ones.
Smaller plants form roots rapidly and become established more quickly than those that are overgrown.

2. Though tomatoes can be planted slightly deeper than the cell-pack, do not bury plant deeply or lay the stem sideways. Though roots will form on the stems of tomatoes, this requires energy that would be better used for establishment and growth.

3. Use a transplant solution (starter solution) when transplanting to make sure roots are moist and nutrients are readily available.

4. Do not mulch until the plant is growing well. Mulching too early prevents soil from warming up.

Borers on Pines?

If you see a row of holes on pine trees, the problem is not borers. Borer holes will be randomly spaced over the trunk. Holes that are in a horizontal (most common) or vertical row are caused by the feeding of the yellow-bellied sapsucker. This woodpecker makes shallow holes and then feeds on the sap released from the wounds or on insects attracted to the site.

Other trees this bird often attacks include maples and Bradford pear, but about any tree species is a potential target. Surprisingly, certain trees may become favorites to the exclusion of nearby trees of the same species. Damage to mature, established trees is usually slight and temporary though small trees may be girdled and killed. To control them, you have a couple of options:

– Wrap the trunk with fine wire mesh in the area of damage. This may discourage them if left in place for several months. The mesh MUST be adjusted every six months or removed when no longer needed. If the mesh is left in place, the tree will likely be girdled.

– Use Tanglefoot on the area of damage. This is a sticky material that is applied to tree trunks to capture insects that crawl up the trunk. Yellow-bellied sapsuckers do not like to put their feet in the sticky material.

Ash/Lilac Borer

If you have had problems with canes or stems of lilac and privet suddenly wilting, or ash trees that show borer holes in the trunk and larger branches, the ash/lilac borer may be to blame. This insect causes the base of infested lilac stems to swell and the bark to separate from the wood. A fine sawdust-like material is present around holes in the canes. Ash and mountain ash also are affected. The borer attacks the trunk, which may cause bark to swell and crack if there are repeated infestations.

Ash/lilac borers overwinter as larvae in infested trees and shrubs. Moths generally begin to emerge in mid to late April. Emergence peaks in May, dwindles by mid to late June and ends by the first week of July. The moth has clear wings and resembles a wasp. There is one generation per year.

Public and commercially managed properties often use pheromone traps to determine the presence of adults. Spray treatments are started seven to 10 days after capture of the first moths. Sprays also can be timed using phenology, the practice of timing one event by another.

The first spray for ash/lilac borer should be applied when the Vanhoutte spirea is in full to late bloom, probably by about May 1 this year (if it blooms). Apply a second spray four weeks after the first. Thoroughly treat the trunk and larger limbs of ash or the lower portion of the stems of lilac or privet. Heavily infested ash should be cut and burned during the fall and winter.

Infested stems of lilac or privet should be removed as well. Permethrin (Hi-Yield Garden, Pet, and Livestock Insect Control) is labeled for control. Though there are a number of other homeowner products that contain permethrin, the product listed above is the only one I’ve found that specifically lists the ash/lilac borer on the label.

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Remove Blossoms on Newly Planted Strawberries

Spring-bearing strawberry plants that were set out this spring should have blossoms pinched off. New plants have a limited amount of energy. If blossoms remain on the plants, the energy that should go to runner development is used to mature fruit instead. For a good strawberry plant population and a good strawberry crop next year, early runner development is necessary. Early developing runners will produce the most strawberries next spring. Newly planted everbearing plants also should have the fruits removed for the first 4 to 6 weeks after planting so they develop a strong root system.

Fruit Tree Sprays and Rain

A spreader-sticker should be used in fruit tree sprays to improve the distribution and retention of fungicides and insecticides on fruit and leaves. However, even with a spreader-sticker, a rain can reduce the length of time the materials are effective. Less than one inch of rain since the last spray will not significantly affect residues. One to two inches of rain will reduce the residue by one half. Reduce the number of days until the next spray by one half. More than two inches of rain since the last spray will remove most of the spray residue. Re-spray as soon as possible. Details on when and what to spray are available in the K-State Research and Extension publication, “Fruit Pest Control for Home Gardens” at http://www.oznet.ksu.edu/library/hort2/c592.pdf

Controlling Weeds in Strawberries

Strawberries are one of the most popular fruits, but gardeners often have problems with weed control. Strawberries form a mat of plants, so hoeing is difficult, and gardeners must pull weeds by hand or use herbicides. Unfortunately, homeowners do not have any weed preventers available for use on strawberries. However, we do have an herbicide that is a grass killer. Poast (sethoxydim) can only be used after the weedy grasses have emerged. Poast can be sprayed directly over the strawberries without harm. Do not use within 7 days of harvest. You can find Poast in Hi-Yield Grass Killer and Monterey Grass Getter.