Presentation on theme: "Things Peanut Growers Should Know About Three-Cornered Alfalfa Hoppers Steve L. Brown Extension Entomologist University of Georgia."— Presentation transcript:
Things Peanut Growers Should Know About Three-Cornered Alfalfa Hoppers Steve L. Brown Extension Entomologist University of Georgia
First, THEY SUCK! They have piercing sucking mouthparts and feed on plant juices. Adults like the one shown have wings and are very mobile.
Nymphs look much like adults except they are spiny and do not have functional wings. They feed in the same manner as adults.
They feed in a circular fashion around stems…
and leaf petioles, and sometimes, pegs
They probe with their stylet and selectively feed from phloem tissue. Phloem is the tissue that transports sugars generated in the leaves.
Damaged phloem results in back up of sugars above the feeding site. Note the difference in stem diameter above and below the feeding site, or girdle.
Under some conditions, the swollen stem may even split open.
Physiological changes sometimes cause the stem to turn purple above the feeding site(s).
Plants with multiple feedings sites can have severely restricted sugar transport. Blooms, pegs and pods beyond a feeding site may be deprived of needed nutrients. Multiple feeding sites are often found on the same stem.
Plants react to damaged phloem in different ways and the reaction will worsen with time. Feeding sites will continue to swell and tissue will decay. The plant will try to bypass the damaged area by developing aerial (adventitious) roots. The damage on the right was probably caused by feeding that happened weeks earlier.
Affects on yield are not well documented but extensive feeding like this is likely to reduce yields.
There is some evidence that feeding sites close to the ground may lead to increased incidence of white mold.
Scars in the stem above the feeding site are egg-laying (oviposition) sites. Eggs are laid in the plant tissue experiencing the back up of sugars, apparently so young nymphs can easily find phloem tissue.
There is a varietal difference in the amount of feeding damage and in the plant’s reaction to feeding damage. In other words, the effect of 3CAH on yield depends upon the number of feeding sites and how the plant responds to that damage.
Variety2003#2004#2005# Avg. (Rank) Hull 15.2a219.2a123.7a119.4(1) A Norden17.0a116.7ab217.7a-c317.1(2) GaGreen14.2a314.0bc319.2ab215.8(3) AndruII7.7b-d711.5b-d515.2b-d411.5(4) C99R11.0a-c49.0c-e812.2c-e510.7(5) DP19.7a-d611.5b-d410.2d-g710.5(6) Carver11.0a-c59.0c-e911.2d-f610.4(7) GA01R5.2cd810.5cd68.5e-g98.1(8) AP35.7cd911.0cd75.0g87.2(9) Avg. # Feeding Sites/3 ft
Other Varieties GA02C – mid to good in 2 tests VA-98R – best among 14 in ’04 Perry – slightly better than AP3 in 2 tests NCV11 – similar to AP3 in 1 test Gregory – mid to poor in 2 tests Tifrunner – middle of pack in ‘05 85A &81R – Similar to GG in 1test
“Low risk” varieties may not need any treatment at all in most years. Higher risk varieties such as Georgia Green should be scouted and sprayed as needed.
Scouting for 3CAH A sweep net is good for sampling adult populations, but not nymphs Flush counts can also be used – count adults flying away as you tap the foliage with a yard stick Nymphs can be dislodged from the foliage in the same manner as foliage feeding caterpillars
Insecticide timing is more important than selection, so scouting is critical to controlling this insect! Early generations are synchronized so nymph hatch out can be targeted. June and July hatch outs must be controlled to prevent the heavy damage and high populations seen in August and September. If you can’t scout, early July seems to be the key time for control most years. But CAUTION, excessive spraying can lead to outbreaks of foliage feeders or spider mites.
Insecticides to Consider Pyrtheroids such as Asana*, Karate and Baythroid – mixed results, do not do well in high temperatures Orthene* – works well, but may flare mites under hot, dry conditions Sevin – works well, but may flare mites under hot, dry conditions Lannate* – works well but, little residual control * 3CAH not listed on peanut label
A Case Where Spraying Didn’t Help Avg. # Feeding Sites / 10 Plants At Harvest – Randolph Co. TotalWithin 3” of crown Karate 1.3 oz X a12.3a Untreated33.6a14.3a Komar,Duffie, Brown ‘03
A Case Where Spraying DID Help TreatmentAdults/10 sweeps Girdles /Plant WM hits/ 100’ Yield UTC9.7 a6.3 a5.0 a5176 b Karate 1.3oz.X2 3.8 a2.0 b2.7 b5555 a Komar, Duffie, Brown Randolph County
Proposed Treatment Thresholds Greater than 75 days to digging – 1 adult per 6 feet of row, or, any nymphs 25 –75 days to digging – 1 adult or nymph per 3 feet of row Less than 25 days to digging – do not spray