Insect and Mite Pest Management in Florida Peanut
Introduction
Peanut (Arachis hypogaea) is one of the most important cash crops grown in the United States, with an estimated production value of over $1 billion. The southeastern coastal plains harbor most of the US peanut acreage from North Carolina to Texas. Florida is ranked among the top five major peanut producers in the United States, with 160,000 acres planted in 2022 and an annual production value of $130 million in 2021 (USDA-NASS). The majority of peanut acreage in Florida is in the Panhandle and central Florida, with Jackson, Santa Rosa, and Levy counties in the top three. Peanuts are affected by several insect pests that feed on various plant parts, including foliage, roots, and fruiting structures. Feeding by these pests can not only cause significant damage to the plant canopy and kernels but can also transmit diseases, reducing the overall quality and quantity of yield if not properly detected and managed. This publication serves as a guide for Extension agents and growers to provide an overview of proper sampling techniques and management for peanut pests found in the Florida Panhandle.
Peanut Pest Insects: Identification Guides
The ability to identify and recognize different insect pests and their associated damage in a peanut field is necessary for pest management. The primary pests of peanuts can be categorized into the following groups: foliage feeders and subterranean (“peg and pod”) feeders. Foliage feeders include thrips, leafhoppers, lepidopteran (moth) larvae, mites, and whiteflies. Subterranean pests include coleopteran (beetle) larvae, lepidopteran larvae, and burrowing bugs (Heteroptera, family Cydnidae). The life cycles of these pests vary and can be driven by climate, crop rotations, and adjacent crops. See identification guides below for life cycle and identification information.
Foliage Feeding Pests
- Tobacco thrips – Frankliniella fusca Hinds
- Potato leafhopper – Empoasca fabae Harris “‘hopper burn”
- Three-cornered alfalfa hopper – Spissistilus festinus Say
- Two-spotted spider mite – Tetranychus urticae Koch
- Silverleaf whitefly – Bemisia tabaci Gennadius
- Corn earworm – Helicoverpa zea Boddie
- Tobacco budworm – Heliothis virescens Fabricius
- Fall armyworm – Spodoptera frugiperda Smith
- Granulate cutworm – Feltia subterranea Fabricius
- Velvetbean caterpillar – Anticarsia gemmatalis Hubner
- Beet armyworm – Spodoptera exigua Hübner
- Southern armyworm – Spodoptera eridania Stoll
- Yellowstriped armyworm – Spodoptera ornithogalli Guenee
- Soybean and cabbage Loopers – Chryodeixis includens, Trichoplusia ni
- Rednecked peanutworm – Stegasta bosqueella Chambers
Subterranean (Peg and Pod Feeding) Pests
- Lesser cornstalk borer (LCB) – Elasmopalpus lignosellus
- Southern corn rootworm (SCW) – Diabrotica undecimpunctata
- Wireworms “peanut wireworm” – Conoderus scissus
- Whitefringed beetles – Naupactus leucoloma Boheman
- Burrower bug – Pangaeus bilineatus
Chemical Control and Economic Thresholds
The best way to manage these insects is to scout fields and treat them only when necessary. Insecticide should be applied only when pest density reaches the economic threshold for a particular pest insect. Although most peanut pests are defoliators, peanuts can compensate for a lot of foliage feeding. When pest density is below the economic threshold, spraying insecticide will do more harm than good and can potentially cause a secondary pest outbreak. For example, organophosphates and pyrethroids are known to increase the risk of spider mite outbreaks after an application. Below, we provide a survey of different sampling methods and current economic thresholds for peanut pest insects when known.
Sampling Methods
Proper sampling methods are vital for getting the best estimates of pest populations within your fields. It is important to sample at multiple locations (at least 10) within a field to get an overall field average. One sampling location may indicate a “hot spot” and may not necessarily represent the whole field. Sketching the field to create a predetermined sampling route to record and visualize the spatial dynamics of the pests in your field is a good practice. Insect populations are generally clumped/aggregated or non-uniform, and spot treatments could be warranted under certain circumstances. Using several sampling and scouting methods across the season at different growth stages will increase the chances of early detection and is a better strategy than is waiting until plant damage or stress becomes visible. Soil sampling before planting (either spade sampling or using seed baits/pitfall traps) can indicate burrower bug and wireworm populations within the field. Once peanut seedlings emerge, you can shift to weekly visual inspection, beat sheet, and sweep netting methods. See descriptions of these methods below.
Visual inspection: Carefully inspect plants (foliage, stem, roots) for signs of insect feeding like hopper burn (v-shaped yellowing on leaflet tips), defoliation, terminal damage, wilted stems, and plant yellowing. Check plant terminals for the presence of thrips in folded leaflets. Check stems for silk tubes (LCB), and pull up plants to inspect roots and fruiting structures for more silk tubes.
Beat sheet/cloth/card sampling: Beat sheets can be used to sample foliage-feeding caterpillars and other pests. A standard sheet is composed of white or black cloth. It should be three feet long and wide enough to fit between rows. Place the sheet at the base of the plants and vigorously shake the plant canopy to dislodge pests. Count the number of larvae per foot of row. Thrips can be monitored with this method, but often thrips will not be dislodged if they are in folded leaflets, which makes visual inspection the better method for detection/accurate counts. Use an index card or laminated sheet of paper to make thrips easier to see. Beat or slap the foliage against the card or paper, and count the thrips that fall off the leaves onto the card.
Pitfall traps: This is a relatively inexpensive way to detect and monitor adult burrower bugs and click beetles (wireworm adults) throughout the season or before planting. Dig a hole in the soil between rows deep enough to place a 12oz plastic cup. Fill the cup one-third full with soapy water or propylene glycol. The rim of the cup should be flush with the surrounding soil so insects will fall into the cup. Check weekly for insects or more frequently if rain is in the forecast. This method will only indicate insect presence in the field. Physical and visual inspection of plant roots and pods will further indicate pest presence.
Germinating seed baits: Seed baits are mainly used for wireworm monitoring/detection before and during the season, especially if a field has had previous infestations. Use a mixture of untreated wheat, sorghum, and corn seeds. Soak the seed mixture for 24 hours before placement. Dig a pit (9 inches wide and 4 inches deep) and put a handful of the soaked mixture into it. Cover the seeds with a shallow layer of soil and place a 15x15-inch piece of a black plastic garbage bag on top. Seal the edges with the surrounding soil. After one week, dig up the seed baits and the soil around and under the seeds, as wireworm larvae appear in both seeds and surrounding soil. Manually sort through the soil and seeds to find wireworms. One bait per 3 acres of the crop may be sufficient to assess the wireworm population in a field.
Spade sampling: Soil samples can be collected with a small spade or soil corer (4- to 6-inch diameter and 4-inch depth). Take samples around the area adjacent to the plant base and sift soil with a mesh screen (size 5–12).
Sweep net sampling: Using a 15-inch-diameter sweep net, briskly thrust the net downward in an arc of about 3 feet perpendicular to the plant rows. Make the sweeps from one side to the other parallel to the ground. While sweeping, pace down the row, taking one sweep per step for 12–15 paces. A sweep net sample consists of 12–15 sweeps as one sample. The sweeps should be vigorous enough to dislodge the insects, and a proper sample will contain leaves. After the 15 sweeps, count the number of target insects and move to another area for sampling.
Pod sampling: Direct visual examination of pods is the most reliable sampling method for soil-dwelling insect detection and injury, such as southern corn root worm, burrower bugs, and wireworms. Start sampling at the beginning of pod development. Check the pods for small to medium-sized circular holes/puncture marks at one end of the pod. Larvae can make a series of entry holes all in one area of the pod. Examine developing kernels for puncture marks from burrower bug feeding as well. Pods can be partially dried to enhance the detection of feeding injury on the kernels.
Cultural Control Practices
In addition to chemical control, there are several cultural control practices used for pest management and for disease management in peanut. These include planting date manipulation, conservation tillage and planting disease-resistant cultivars. Planting date manipulation is one of the few available options for tobacco thrips management and Tomato spotted wilt virus (TSWV). In the Southeast, the planting window for peanuts is normally from April to June and shifts slightly each year depending on environmental conditions, which also affect thrips populations. Studies have shown that thrips populations and TSWV are both greater in April-planted peanuts compared to May- or June-planted peanuts, and thus the optimal time to plant is from May 10th through May 31st throughout the Southeast. Conservation tillage systems such as strip tillage are another cultural control practice that reduces thrips populations and risk of TSWV. Crop or cover crop residue is thought to interfere with the thrips’ ability to find the host plant (peanut). For more information on conservation tillage, see the publication Producing Peanuts Using Conservation Tillage. For more information on other cultural control practices and peanut production, see the publication Management and Cultural Practices for Peanuts and visit the Florida Peanut Team webpage.
Table 1. Sampling Methods and Action Threshold per Pest.
Table 2. Florida Insecticide Options in Peanut. Contact: Isaac L. Esquivel, Field and Forage Crop Entomologist (Isaac.Esquivel@ufl.edu). This table lists registered pesticides that should be integrated with other pest management methods. Contact your local UF/IFAS Extension office for additional information (https://sfyl.ifas.ufl.edu/find-your-local-office/).
