Posts tagged insecticide

Not so sweet pest

Entomologist Donald Lewis, of Iowa State University Extension, offers the following information about the bane of sweet corn:

One of the pure pleasures of summertime in Iowa is eating sweet corn fresh from the garden or farmers market. To the dismay of gardeners, growers and sweet corn aficionados, however, there is the matter of an occasional pest to consider. The most important and best known insect pest of sweet corn in Iowa is the pudgy, hairless “worm” found at the tip of an infested ear, the corn earworm.

Corn earworms come in a variety of colors, ranging from light green, to tan, brown, pink or nearly black. The caterpillar’s body is marked with light and dark stripes running lengthwise and the skin texture is coarse due to microscopic spines that cover the surface.  Earworms are only in the ear for three to four weeks but during that short time they grow to nearly 1 .5 inches in length.  Infestations may be present throughout the summer but are generally worse in late summer.

Unlike hardy residents of the state the corn earworm does not survive Iowa winters.  Instead moths that lived and grew in southern states on either corn or cotton last year are blown here during May and June each year to reinfest the state.

These recent-arrival-moths fly after sunset and reproduce by depositing their eggs on the fresh, green silks of the sweet corn ear. These eggs hatch in two to six days and within an hour the tiny, young larvae crawl into the silk channel and move to the tip of the developing ear. The larvae feed on the silk and developing kernels and foul the ear with excrement.  About three weeks after silking the sweet corn is ready to harvest and eat, and there, waiting for you at the end of the ear is the much-grown earworm caterpillar.

The amount of corn earworms in the sweet corn crop varies from place to place, from year to year and with the time of the year.  Mostly the damage is determined by the number of moths in the vicinity which depends on the weather and other factors. Some varieties of sweet corn are more or less susceptible to earworm attack, and genetically modified varieties are available that produce their own defense against caterpillar attack.

Growers and gardeners who want “clean” sweet corn must work to prevent the earworms from getting into the silks. If the caterpillars are already crawling toward the ear tip it is too late to stop them. A typical preventive management strategy is to spray insecticide on the corn ears throughout the entire period when green silks are present. 

Insecticides for the home gardener include azadirachtin (Neem), Bacillus thuringiensis, carbaryl (Sevin), or permethrin. Spray at the first sign of silk emergence (one or two days after tassels appear) and again two days later after silks have elongated. For complete protection, especially in later plantings, spray a third time three days after the second spray.  After the silks turn brown there is no benefit to spraying.  

Admittedly, this is an extensive amount of insecticide but it is currently the most practical method for assuring worm-free sweet corn.  The alternative is to not treat at all.  Instead, cut off the damaged tip of infested ears and enjoy the remainder of the ear.

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How much rain is enough and more gardening tips

Linn County Master Gardener Claire Smith describes how much water is enough  (obviously, many parts of Iowa have had too much this week) and other gardening hints:

 

We’re so excited:  my favorite daughter’s garden is growing by leaps and bounds.  We had no idea of the quality of soil in the area, but luckily she unknowingly over seeded so we can do some thinning.  Her husband is excited to be able to walk out and pluck a ripe tomato.  Can you imagine the kids learning to hull peas?

So how is your garden growing? 

Have you noted your guests—your birds and butterfly buddies?  Adding bird and butterfly houses and water may encourage them to stay longer.

Keep planting. Try a new variety.   “Mudding” in plants is not a great idea, but there are certainly a variety of perennials still available when the ground dries out a little. 

Due to the overly wet conditions now, it’s a good idea to check your plants for mold and mildew.    Remove any leaves with blotches or that are discolored.  Use an insecticide soap to control insects.  Wet conditions do make weeding easier. 

Perennials generally do not need extra fertilizer.  The soil usually provides adequate nutrients.  Watch your plants, though and if they need a boost, go ahead with a liquid fertilizer. 

Perennials require one inch of water each week.  New plantings will request water several times each week.  It is better to water thoroughly less often.   Young new trees should be checked routinely and watered thoroughly as needed.  Remember clay soils retain water:  sandy soils do not. 

Finish pruning spring-flowering shrubs this month.  Prune so that the top of the hedge is narrower than the bottom to allow light to reach all parts of the shrub. 

Deadhead annuals as soon as the flowers start to fade to encourage new growth.

               

And, remember to plan a fun, educational and inexpensive ($10 for the entire family!) day on Saturday, June 14,  from 10 a.m. to 3 p.m. at the Linn County Master Gardeners’ First Annual Garden Walk.  Tickets are available at each location.  For more information, see the last two weeks’ blogs or call the Horticulture Hotline at 319-447-0647. 

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Bad “worms”

Iowa State University Extension gardening experts answer questions on damaging worms:

 

Worms are devouring the needles on my mugo pine.  What should I do?

 

The “worms” that are eating the needles on your mugo pine are the larvae of the European pine sawfly. European pine sawfly larvae are grayish green. Two light stripes and one dark stripe run down the sides of the body. The legs and head are shiny black. 

 

The larvae feed mainly on mugo, Scotch and Austrian pines, though other pine species are occasionally damaged. They do not feed on spruce or fir. Larvae typically appear in mid to late May in Iowa and are usually gone within a few weeks. 

 

European pine sawfly larvae feed on needles produced in previous years. (The needles on most  pines persist for two to five years.) They do not harm the new needles developing on the branches. As a result, the damage is mainly aesthetic. Larval feeding does not destroy the affected branches. The branches simply have fewer needles than normal. 

 

To keep damage to a minimum, the larvae of the European pine sawfly can be controlled by pruning off and discarding infested branches, knocking the larvae off affected branches into a bucket or other container and destroying them, or spraying them with an insecticide, such as Sevin. 

 

I occasionally find small, white worms in my cherries.  What is the best way to control them?

 

The small, white “worms” are probably the larvae of the cherry fruit fly (Rhagoletis spp.)  Cherry fruit flies lay eggs on developing cherry fruit in May. Damaged fruit appear shrunken and shriveled when ripe, and usually contain one off-white larva (maggot) that is slightly longer than one-quarter of an inch.

 

Cherry fruit fly damage varies greatly from year to year. It may be more practical to tolerate some damage and loss of usable fruit than to attempt effective preventive control.

 

To prevent maggots from appearing inside the fruit, the tree must be thoroughly sprayed with a labeled insecticide when the adults emerge and before the females lay their eggs inside the young fruit. Because the flies emerge over an extended period of time, several sprays will be needed. You can monitor fruit flies with yellow sticky traps hung in the tree in early May. Check traps daily after the first fruit fly is caught and repeat the spray application until flies no longer appear. 

 

Check for home orchard sprays and other insecticides at your local garden center. Carefully read and follow label directions.

 

 

 

 

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White grub watch

The following information is from Donald Lewis, Iowa State University Extension entomologist. For more information from Lewis on grubs, as well as insects,  see the Feb 3 “Lightning bugs eat WHAT??” blog post.

 

Spring is here and the grass looks as good as it is going to look all summer. Since you want to keep it that way you have probably been considering treating for white grubs, either because you have experienced white grub damage in the past, or your friends and neighbors have complained about white grub damage, or a lawn care salesperson’s pitch got you a little excited if not a little scared. Put the insecticide down and step away from the sprayer. We need to talk.

 

Biology and Habits

The white grubs that routinely damage lawns in Iowa are called annual white grubs. These root-eating, underground June beetle larvae have one generation per year and take one year to complete their life cycle of egg, larva, pupa and adult. The adult beetles of our annual white grubs are specific kinds of June beetles called masked chafers. They are tan or straw brown in color and as the name implies, they have a black stripe across the eyes and face. The masked chafers begin flying in late June and lay eggs in the turf during July.

 

The eggs hatch in two to three weeks and tiny white grub larvae begin to eat the grass roots. The grubs grow rapidly and are fully grown at one inch in length by late August or September. White grubs are pudgy, off-white except for the brown head and typically bent in the shape of the letter “C.”  Feeding by the grubs prunes the roots from the plants and causes the grass to wilt and fade. 

 

Extreme feeding by populations of 10 or more annual white grubs per square foot will cause the grass to die. White grubs move several inches deep in the soil to spend the winter. They move back near the surface in the spring time but cause little additional damage as they wait to pupate in June, emerge as adults and start the cycle over.

 

Management Options 

White grub populations and damage to lawns vary greatly from year to year and place to place, even varying from spot to spot within the same lawn due to variations in beetle numbers, weather, turfgrass vigor, soil conditions and other factors. There is no method that predicts if and where grubs will occur or how severe the damage will be. What happens in your lawn this summer is a random event and not directly tied to previous experience. Therefore, decisions concerning white grub management are difficult; there is no one right answer for everyone.

 

There are three basic approaches to grub management in the home lawn, depending on your tolerance for damage, comfort with pesticides and willingness to spend the cash. White grub insecticide treatments are not only expensive but hard to justify from an environmental standpoint.

 

In places such as golf courses and some lawns, the risk of any white grub damage is so intolerable that preventive insecticides are applied to every part of the lawn, every year. When this approach is chosen, the proper time of application is between early June and Aug. 15. A compromise modification of the golf course approach is to treat only those areas that have been previously damaged. Beetles tend to return to the same areas in successive years, so it is logical to treat the areas where the grubs were last year or the year before.

 

The second approach is the wait-and-see approach. Watch the lawn carefully for early signs of damage (wilting, turning brown) during August to early September when grubs could be feeding. Apply a curative insecticide only where and when needed. The risk is that you might still lose some sod, especially if summer rainfall or irrigation keeps the grass growing and vigorous through July and August. Damage symptoms may not appear until after it is too late for effective treatment (late September through late October).

 

Unfortunately, raccoons and skunks are much better at locating grub populations than we are and the first symptom of a grub problem in your turf is likely to be that your lawn was “plowed” by varmints overnight.

 

The final alternative is to do nothing. This may be easier to do if you count up how many years you DID NOT have grub damage. Divide the cost of replaced sod by that number of years. If the yearly-averaged cost is less than the price of insecticide, do nothing and take your lumps in the occasional year when damage occurs. This approach is much easier to follow if you believe “it’s just grass, anyway.”

 

White grub management decisions are difficult and frustrating. Many homeowners are frightened into applying grub controls because of advertisements on TV, in plant centers or because of horror stories they have heard about grub damage. Studies at Cornell University have shown that more than 70 percent of all grub control treatments were applied needlessly because there were no grubs in the lawn.

 

If you do choose to apply insecticides, read the application directions carefully before buying. Some grub treatments are preventive and must be applied before mid-August. Others are curative and work only if the grubs are present. Know which you are getting before you buy. Apply carefully according to label directions and thoroughly water in the insecticide. Watering accomplishes two things: it moves the insecticide into the soil where the grubs reside, and it removes the active ingredient from the surface and greatly reduces the hazard of insecticide exposure to people, pets and wildlife walking on treated turf.  Irrigate the treated area with at least one-half inch of water.

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