By Katie Nichols
There are beneficial insects who take up residence in cotton fields, and then there are damaging pests, like the grasshopper, who create problems for cotton producers.
Alabama Cooperative Extension System entomologist, Dr. Ron Smith, said grasshoppers have been sporadic seedling cotton pests for more than 10 years.
A well-known fable about an ant and a grasshopper depicts the ant as hard working and the grasshopper as lazy. However, Smith said when it comes to cotton crops, both are hard working, but grasshoppers are hard at work damaging cotton crops.
Fire ants make their home in cotton fields and are hard-working pests. They feed on caterpillar pests, like bollworms and other pests detrimental to cotton crops. In contrast to their lazy nature in the fable, grasshoppers make quick work of damaging seedling cotton stands.
Grasshoppers Feed on Seedling Cotton
“The grasshopper problem emerged as a result of the conservation movement to reduced tillage,” Smith said. “Certain seasons seem to be worse than others, and 2018 has resulted in greater concern than more recent years.”
Growers reported high numbers of adult grasshoppers at harvest during the fall of 2017. Smith said overwintering populations are influenced by environmental conditions.
“Rainfall is likely more important than temperatures,” he said. “Dry winters are favorable for grasshopper populations since they overwinter as eggs in the soil.”
However, grasshopper problems are sporadic and nearly always associated with reduced tillage fields.
Grasshopper Lifecycle and Development
The primary crop-damaging grasshopper is the differential species, which also overwinters as eggs in the soil. Eggs hatch from late March through April, May and June as soil temperatures rise and spring rains fall.
The first nymph to leave the egg pod makes a tunnel from the pod to the soil surface through which the following nymphs emerge. Nymphs feed and grow for 35 to 50 days before becoming adults. Adults can fly, while nymphs or immatures can only jump.
Smith said their development progresses most rapidly when the weather is warm, but not too wet. Mature grasshoppers mate and continue feeding on plants. About two weeks later, females begin to deposit clusters of eggs in the soil. Soil particles are glued together around the eggs to form a protective pod. Each pod may hold 25 to 150 eggs. Most grasshopper species only complete one generation per year.
Hoppers Prefer Sandy Soil
Smith said grasshopper-related issues are greater in lighter soils, or soils with higher sand content. Damage often occurs in the same fields or on the same farms from year to year.
While damage is unpredictable, it could potentially threaten a stand. Grasshoppers may feed on foliage, but most economic damage occurs when grasshoppers feed on the main stem of emerging seedlings. This includes cotton in the crook or cracking stage.
“In some cases, grasshoppers may completely sever the stem, but more often they will chew partially through the stem,” Smith said. “This weakens the plant, which will fall over at the feeding site.”
Field Treatment
Smith said growers with long-standing grasshopper problems may want to take a more preventative approach by adding in a grasshopper insecticide during the burndown herbicide application. Since not all grasshoppers emerge from the egg stage at the same time, a long residual insect growth regulator insecticide could also be utilized.
“There are no established thresholds for grasshoppers in cotton—and likely will never be—since their feeding habits are so unpredictable,” Smith said. “Some fields and some years may have grasshopper damage while other fields and years have the same level of pest presence, but no damage.”
He said preventative insecticide applications for grasshoppers are a judgment call. When grasshoppers are observed and cotton is in the susceptible stage, treatments can be based on the risk level that an individual grower is willing to take.