Grasshopper: Sporadic Pest of Seedling Cotton

Grasshoppers have been a sporadic pest of seedling cotton for 10 or more years. Growers reported observing high numbers of adult grasshoppers during harvest season in fall 2017. Overwintering populations are influenced by environmental conditions. Rainfall is likely more important than temperatures. Dry winters are favorable for grasshopper population since they overwinter as eggs in the soil. Grasshopper problems are sporadic and almost always associated with reduced tillage fields.

The primary grasshopper that damages cotton is the differential species which also overwinters as eggs in the soil. Eggs hatch from late March throughout April, May and June as soil temperatures rise and spring rains occur. The first nymph to leave the egg pod makes a tunnel from the pod to the soil surface through which the succeeding nymphs emerge. Nymphs feed and grow for 35 to 50 days before becoming adults which can then fly. The nymphs or immatures can only jump. Their development proceeds most rapidly when the weather is warm but not too wet. Mature grasshoppers mate and continue feeding on plants. About 2 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 have 25-150 eggs. Most grasshopper species only complete one generation per year.

In fields with historical grasshopper problems, growers may want to take a more preventative approach by adding a grasshopper insecticide to their burn down herbicide. Since not all grasshoppers emerge from the egg stage at the same time, a long residual IGR (insect growth regulator) insecticide could also be utilized. Dimlin has proven to be a good management tool for grasshoppers. It has extended residual that provides good control of immature grasshoppers but will not control adults.

There are no established thresholds for grasshoppers in cotton and will likely never be since their feeding habits are so unpredictable. Some fields and some years may have grasshopper damage while other fields and years have the same level of grasshoppers but no damage. 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.


Grasshopper problems are greater in lighter soils or soils with higher sand content. Damage often occurs in the same fields or farms from year to year. Grasshopper damage as stated is unpredictable but can potentially threaten a stand. Grasshoppers may feed on foliage, but most economic damage occurs when grasshoppers feed on the main stem of emerging (in the crook or cracking stage) seedlings. In some cases, grasshoppers may completely sever the stem, but
more often they will chew partially through the stem weakening the plant which will fall over at the feeding site.


Most all cotton insecticides will control immature grasshoppers when applied at a low labelled rate. Later into the spring, adult grasshoppers are very difficult to control with any insecticide, even at a high labelled rate. Acephate (Orthene) at 0.6 lb. active per acre has proven to be the most effective grower treatment for adult grasshoppers.

Early Season Thrips Control Important

Cotton planting and early season thrips management are almost upon us. We are fortunate today to have varieties that have three-plus bale yield potential. While we can’t control rainfall patterns for 2020, we can make sure that other factors such as early season insects, especially thrips, do not stunt or delay growth and development of seedling cotton.

Seed treatments alone are not as effective as in-furrow granular insecticides used in the past. Because the seed treatments imidacloprid (Gaucho) and thiamethoxam (Cruiser) have lost some or much of their effectiveness due to insect resistance, we are forced to add additional thrips-suppressing measures such as in-furrow or foliar sprays in our management programs. Research has shown that foliar thrips sprays are most effective when applied at the 1^st true leaf stage or very shortly thereafter. Such treatments on early planted cotton may be needed before growers finish planting later fields. Furthermore, an initial, timely spray may be most beneficial even before the 1^st true leaf has visible thrips injury.

We now have a tool that helps us know when this first foliar spray may be most effective. This tool is a Thrips Prediction Model. It is quite accurate in forecasting thrips pressure based on planting date and local weather. The model can be accessed at climate.ncsu.edu/cottonTIP. To indicate your farm location, scroll across the map to your site and click to drop a red pin. You then select anticipated planting date. The model accesses nearest weather station information for temperature and rainfall, data which enable predictions about the growth of seedling cotton as well as the status of wild hosts that serve as sources for thrips migration.

We have determined that thrips migration from adjoining hosts can peak early, mid, or late in the planting window. Since weather is a big factor in both seedling growth and the dry-down and maturity of wild hosts, the accuracy of the model improves when it is used as close as possible to the actual planting date. The model color codes the level of predicted thrips injury:  GREEN=low pressure, YELLOW=moderate pressure, or RED=high pressure. Based on 2019 experiences, a model prediction of RED indicates that an automatic foliar spray will be necessary, even before leaf symptoms are evident.

Insecticide choices for foliar thrips treatments are listed in the Extension Cotton IPM Guide – IPM-0415. They include acephate (Orthene or generics), dicrotophos (Bidrin), dimethoate (or generics), and spinetoram (Radiant or Intrepid Edge, which contains Radiant).

Since the model will likely contact the same weather station even if you plant in multiple counties, it makes sense to simply use one pin as your farm location. However, it is beneficial to run the model with varying planting dates, probably at least once every 7 days. Different regions of the state (North, Northeast, Central, Southeast, Southwest) may have significantly different thrips pressure as occurred in 2019.

To increase our chances of profit for 2020, we need to begin the season with the goal of producing the highest possible yield. Insect-wise, this begins with preventing the yield robbing and delaying effects of thrips injury.