Henderson Co. Agriview
by Rick Hirsch

Grasshoppers are among the most widespread and damaging pests in Texas. Approximately 150 species of grasshoppers are known to exist in the state; however, only five species cause 90 percent of the damage to crops, gardens, trees and shrubs.

These insects cause some damage every year, but become very destructive during outbreak periods. An often asked question during outbreak years is: Why are there so many?

Weather is the main factor affecting grasshopper populations. Outbreaks are usually preceded by several years of hot, dry summers and warm autumns. Dry weather increases nymph and adult survival. Warm autumns allow grasshoppers more time to feed and lay eggs. Cool, wet weather slows nymphal development, reduces the number of eggs laid, and increases the incidence of diseases.

Grasshoppers have a high reproductive capacity. The female can lay an average of 200 eggs during a single season. Under favorable conditions, up to 400 eggs can be laid. Approximately 40 eggs can be laid even if unfavorable conditions exist. Thus, 10 times more eggs can be produced during favorable conditions. With an average of 200 eggs per female, 198 eggs or young grasshoppers would have to die if the population were to remain the same. If, instead of only two adults surviving, there are four, six, eight, ten or fifty then the adult population the following year will be increased two, three, four, five or twenty-five times, respectively.

Farmers and ranchers should watch for grasshoppers early in the season and begin control measures while grasshoppers are in the nymphal stages and still within hatching sites (roadsides, fence rows, etc.). There are a number of advantages in treating grasshoppers early: 1) fewer acres will have to be treated and less insecticide is necessary to obtain control; 2) grasshoppers are killed before they have had the opportunity to cause significant crop loss; 3) smaller grasshoppers are more susceptible to insecticides than larger hoppers; 4) early treatment before grasshoppers reach maturity prevents migration of the winged (flying) adult stage and egg laying, which may help reduce the grasshopper threat for the following crop year.

Grasshopper infestation levels can be estimated by surveying for nymphs or adults. One method is the square-foot method. In the area to be sampled, count the number of grasshoppers that hop or move within a square foot area. With 15 to 20 paces between each square-foot sample, conduct 18 squarefoot samples and divide the total number of grasshoppers by two to obtain the number per square yard. If the grasshoppers are predominantly first to third instar, (wingless and generally less than 1/2- inch long), divide the number by three to give the adult equivalent. Consider fourth instar nymphs and above as adults. Control will generally be necessary when squareyard counts reach the threatening level of 21 - 40 in the margins or 1 - 14 in the field.

When grasshopper populations reach intolerable levels, or when crops are threatened, a treatment program may need to be considered. You can contact the County Extension Agent or your Ag retailer for more information on recommended insecticides.

PROFIT-ROBBING HORN FLIES:

There are numerous fly species that prey on livestock, such as stable flies, horse flies, face flies and horn flies. Of these pests, the horn fly is the most economically damaging to the cattle industry, causing annual losses in excess of $876 million.

Horn flies breed in fresh cow manure from early spring to the fall and the larva requires an undisturbed fecal patty for development. Populations usually peak in the late spring and again in the late fall.

Researchers consider 250 flies per adult animal to be an economic factor, but with horn flies, thousands may infest a single animal.

Horn flies are blood suckers, feeding up to 40 times a day and spending its entire adult life on the host. This is very irritating and annoying to cattle. The annoyance interferes with the cows' feeding and resting, causing reduced weight gains and lower milk production. Heavy fly populations can reduce calf gains up to a quarter of a pound per day, resulting in a $15 or more loss per calf.

Horn flies prefer cattle as a host but also affect horses, sheep, and goats. They are usually found on the back of the animal host, congregating at the withers, between the front shoulders, but move around to the sides and belly during the hotter or cooler times of the day.

Treatment can be accomplished by applying insecticides with spray, pour-on, dust or fly control ear tags. There has been some resistance build-up over the years with pyrethroid ear tags. If this is the case, rotation of pesticides should be considered, but make sure you are changing the active ingredient and not just the tag color.

Also, to help with resistance build-up, remove tags as soon as possible once they have lost their effectiveness, usually after four or five months. Tags emitting reduced doses seem to add to the resistance problem by prolonging fly exposure, thus making the surviving population more resistant to the insecticide.

Recently, there has been research with animals that are more resistant than others to horn flies. If this is inherited, then fly resistance may become a trait that is looked at when selecting and breeding animals in the future.

The horn fly is one of the more easily controlled pests because it never leaves the host. So, with control, producers can increase the herd's weight gains and profit while giving the cattle a break from these annoying pests.

IMPORTANT DATES:

June 18 & 19 - District 5, 4-H Horse Show, Henderson County Fair Park Complex

June 28 - Horticultural Field Day, 8:30 a.m., Overton

QUESTION OF THE WEEK:

Q. What causes my tomato leaves to curl?

A. The exact cause of this tomato leaf roll is not fully known. Tomato leaf roll appears about the time of fruit setting. The leaflets of the older leaves on the lower half of the tomato plant roll upward. This gives the leaflets a cupped appearance with sometimes even the margins touching or overlapping. The overall growth of the plant does not seem to be greatly affected and yields are normal. This condition appears to be most common on staked and pruned plants. It occurs when excessive rainfall or overwatering keeps the soil too wet for too long. It is also related to intensive sunlight which causes carbohydrates to accumulate in the leaves.

(Rick Hirsch is the Henderson County Extension Agent-Agriculture for Texas Cooperative Extension. Visit his web page at http:// henderson-co.tamu.edu)