Category Archives: Entomology

Managing Silverleaf Whiteflies In Cotton

Probably the biggest agriculture pest topic last year, whiteflies became a problem very fast. Because of our warm winter, white are already present, likely meaning another bad year. The goal in silverleaf whitefly (SLWF) management is to initiate control measures just prior to the period of most rapid pest population development. UGA Extension Entomologists Dr. Phillip Roberts and Dr. Mike Toews put together some info on SLWF:

Risk for SLWF

  • Hairy leaf > smooth leaf cotton.
  • Late planted > early planted cotton.
  • Hot and dry > rainy conditions.

Scouting

SLWF adults (solid white wings) and immatures will be found on the underside of leaves. SLWF populations are best estimated from the 5th main stem leaf below the terminal. Main stem leaves are attached directly to the main stem by their petioles. The top or first main stem leaf is defined as the uppermost leaf which is 1 inch or larger in diameter. Adults and nymphs should be counted on the 5th main stem leaf below the terminal.

Adult whitefly in our UGA On-farm Variety Trial on June 29th. Leaves are considered infested when 3 adults are observed. (This counts adults that fly off when leaf is turned over.

SLWF Threshold

Treat when 50 percent of sampled leaves (sample 5th expanded leaf below the terminal) are infested with multiple immatures (≥5 per leaf).

Leaves are considered infested if 5 immatures are observes.

Insecticides

Insect Growth Regulators (Knack and Courier): use of IGRs are the backbone of SLWF management programs in cotton. Effects on SLWF populations are generally slow due to the life stages targeted by IGRs, however these products have long residual activity and perform very well when applied on a timely basis.

Use of other insecticide options which are active on all life stages have quicker effects on SLWF infestations but lack the residual of IGRs.

SLWF is an areawide cross commodity problem. When all parties use sound SLWF management programs all will benefit.

Steps for Efficient Sampling of SLWF

  1. Familiarize yourself with the general location of the 5th main stem leaf in each field.
  2. Select plants at random at least 25 paces into the field and at least 10 paces apart, being careful to keep your shadow from passing over the plant you plan to sample.
  3. Turn the 5th leaf over slowly by its tip or petiole and count the leaf as infested with adults if it has 3 or more adults on it. Include in your counts any adults that fly up from the leaf as you turn it over.
  4. Detach the leaf by the petiole from the main stem. If it fails to snap off easily, you have likely sampled a leaf that is too high on the plant. Recheck your leaf position to make sure you are sampling the 5th leaf.
  5. Examine the bottom of the leaf for the presence of immature SLWFs. Count the leaf as infested if it has 5 or more immatures on the underside of the leaf. Sample at least 30 plants (leaves) per field.
  6. Calculate the percentage of leaves infested with adults and the percentage of leaves infested with immatures.
  7. Treatment is recommended when 50 percent of sampled leaves are infested with immature SLWFs.

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Filed under Cotton, Entomology

Aphid Fungus

For the first time, I am getting to see what ‘consistent aphids’ looks like in the field. Normally, aphid populations are sporadic, seen only in ‘hot spots.’ This season, they are prevalent in our oldest and youngest cotton. We looked at a field this week where every single plant was affected by aphids in the top 3 – 4 leaves (below). The only reason we don’t talk much about it is UGA research on treating aphids has never found a consistent yield response. The best thing is to limit stress on the plant, and our rainfall is helping us here.

Leaves of 8-leaf cotton curl due to stress of aphids

Classic symptoms of aphids in our cotton variety trial.

Aphid Fungus

But the real new is that yesterday, we confirmed the ‘aphid fungus’ in Thomas County. UGA Extension Entomologist Dr. Phillip Roberts already reported the ‘aphid fungus’ being spotted in Tifton this week. This means, aphids will soon crash.

We observed the aphid fungus, (Neozygites fresenii), which causes aphid populations to crash on the Tifton Campus on June 26, 2017.  We have also received some early observations from both north and south of Tifton.  The presence of grey, fuzzy aphid cadavers is indicative of the naturally occuring fungus (below).  Once observed in the field we would expect aphids to crash within a week.  We typically first observe the fungus in fields with high aphid infestations; and more specifically areas of those fields which were initially infested.  All scouts should be on the lookout for the fungus and be sure to report to growers.

Aphid fungus – Photo by Dr. Phillip Roberts

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Cotton Irrigation At Squaring

Some of our pivots have not been running these past few weeks thanks to steady rainy days. For being so dry at planting, this is hopefully going to get us off to a good start in the field. Below is a photo of rep 2 from our variety trial. We have some plants squaring already.

Remember, stressing cotton during squaring has more negative effects than we realize. Cotton does not rebound if stressed from no irrigation through squaring. Last year, we lost so many squares from drought stress. This is something UGA Extension Irrigation Specialist Dr. Wes Porter says we have to be careful about.

Data on this using the UGA Checkbook Method where pre-bloom irrigation was eliminated found no difference in non-irrigated cotton. The reason for this is that cotton grows vegetatively and reproductively at the same time. During its vegetative growth, cotton is setting nodes. If it is stressed during this time, less nodes are set.

ImpactofPre-BloomIrrigation-J.Whitaker-2012

Dr. Porter has been looking at soil moisture sensors and the irrigation apps we can download on our phone. Research does show that the Smart Irrigation App is keeping us from putting out more water than is needed during both drought and rainfall situations. This is interesting because these apps do not monitor soil moisture, and the Smart Irrigation App is no charge to download. We go one step further when we use soil moisture sensors.

UGACheckbookMethod

Aphids???

I saw some ants crawling up some plants. I then checked for aphids. The ants eat the ‘honeydew’ produced by the aphids, called ‘farming aphids.’ UGA Extension Entomologist Dr. Phillip Roberts says there are some aphid hot spots that may develop in fields now. We just need to watch.

Aphids under leaf of squaring cotton

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Cotton Coming Up, Variety Trial Planted, Scout Thrips

Cotton is anywhere from just planted to cotyledon to 4 leaf at this time. Recent rains have growers planting and we hope to have more this weekend. It’s past our thrips date of May 10th and we have reason to believe thrips may crash soon this year – since we had a warm winter, they were active sooner. But remember, thrips live in the winter weeds along roadsides and move to our cotton and peanuts following germination.

From 0 to level 5, I’m seeing damage from none to about level 3, sporadic in most fields. Neonic seed treatments (imidacloprid, thiametoxam) are active on thrips for up to 14 – 21 days after planting. If we have no seed treatment, we need to be in the field checking the first true leaf. This is the best time when we need to apply a foliar application. Once we have 4 true leaves and the plant is growing fast, thrips foliar sprays are not economical.

Thrips injury on 1st true leaf

Threshold

Research has shown that foliar applications are still needed when thrips infestations are high. The best way to make this decision is based on current threshold of: 2 – 3 thrips per plant AND/OR presence of immatures. The immature (wingless) thrips will be yellow/green in color; the adult (winged) thrips are black. Take a white piece of paper and slap a plant on it. Give it a second for the thrips to start crawling. In this field, I have immature thrips present. This suggests are at-plant insecticides are no longer active, and reproduction is taking place.

Here is a note from UGA Extension Entomologist Dr. Phillip Roberts from 2016. It may still answer some question today:

Should we follow with a second acephate spray? Dr. Roberts has conducted trials with 1 +3 leaf sprays, and they showed no difference from a 1 leaf ONLY spray. Something I noticed rating our thrips trials (2016) is not only the effectiveness of 1 leaf sprays, but also how fast the plants grow in 14 days. If we have a timely insecticide spray, AND growing conditions are good, cotton will outgrow potential thrips issues. The only reason to consider a second foliar application is if 1) cotton is not growing fast 2) thrips are still highly active. It would be a judgment call at best.

How long does this foliar spray of orthene last? Research entomologist Dr. Michael Toews, and Dr. Roberts have data on this that hasn’t been totally put together, but the best analysis is maybe 3 -4 days. Pyrethroids, on the other hand, photodegrade fast. Dr. Roberts says pyrethroids will kill thrips, but the reason we do not recommend them is 7 days after treatment, thrips populations are higher where pyrethroids were sprayed than where orthene was sprayed.

We were able to plant our variety trial last Friday. I visited the field today, and cotton is just now coming up. The field is at the end of Centennial Road where it touches Airline Road. It is the one on the right. We ended up participating in the UGA On Farm Variety Trial. Most of the varieties I asked for were in the trial. We were able to get in all varieties I wanted plus these for a total of 15. We replicated three times in the field; reps are actually stacked on top of each other.

2017 UGA On-Farm Variety Trial

We got done real fast, thanks to Brandon’s precision planting. Thanks to growers Mike, Brandon and Chandler Barnes for planting the trial this year and Jodie Stringer (Boston Gin) for helping and Jessica Jones, owner of Barbaritoes, for feeding us in the field.

Jodie and Brandon fixing flags

Brandon Barnes, Mike Barnes, Chandler Barnes, Jodie Stringer, Andrew Sawyer

 Jodie and Brandon fixing flags

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Satsuma Insect Issues

This may not be the case everywhere, but here we avoided some serious freeze injury on our 3 year old trees. These satsumas are going on 4 years old, so next year is the year we hope to harvest these. Some of these fruit are pulled off the tree this year to allow the tree to focus on vegetative growth.

Leafminers

We haven’t been hit too much with leafminers here, but in other parts of the county and with younger trees, damage is evident. It’s difficult to drench imidacloprid to time killing the initial infestation. Lowndes County Ag Agent Jake Price says this about leafminers and leaf footed bugs:

Leaf miners are starting to emerge. Usually our first flush is safe from leaf miners but they can be a problem at the end of the first flush and every flush thereafter. If you had frost damage and your trees are flushing again, you may want to go ahead and make a treatment. Imidacloprid drenches last about two months. Micromite and Ari-Mek are also labeled to control leaf miners if you are having issues with mites as well. If you do make a foliar application of anything, try to wait until all your blooms are gone as to protect the bees.

Mining trail from leafminer fly. Egg is laid on leaf. Larvae hatches and goes under leaf cuticule where it mines, curling the leaves and comes out to pupate. This one came out where my thumb is.

Leaf-footed Bug

A second insect I have been seeing is the leaf footed bug or what many call “stink bugs”. They can damage fruit and cause them to drop from the tree.  Now they are feeding on young blooms and shoots. I see these insects on a variety of things from muscadines, cotton, soybeans, peaches, plums, and blueberries, etc. They tend to congregate on certain trees. In general, I do not think these are a major pest of Florida citrus but they look like they will be a problem in satsumas because they damage fruit.  Again thoughts are no control is needed at this time unless you just have them throughout your grove.  If needed you may want to treat certain trees where they tend to congregate.

Leaf-footed bugs – Photo: Doug Collins

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2017 Sugarcane Aphid Management In Grain Sorghum

Sugarcane Aphids

Here is the newest management prodecdures for sugarcane aphids in grain sorghum from UGA Extension Entomologist Dr. David Buntin:

1) Plant early – Because the aphid migrates northward in the spring, early plantings may avoid may avoid very large infestations.   Late planted double-crop plantings are at greater risk of severe infestations.   

2) Plant a tolerant hybrid/variety – Some hybrids have been shown to have some partial tolerance to the aphid.   This table from the Sorghum checkoff program and ratings for the Georgia Statewide variety trial lists grain sorghum hybrids with some degree of tolerance to SCA.   In my own trials the most tolerant grain types were in alphabetical order Alta AG1201, Dekalb DKS 3707 and DKS 4807, Pioneer 86P20, Sorghum Partners 73B12 and Warner W-7051 (tall, late variety).

http://www.sorghumcheckoff.com/farmer-resources/grain-production/hybrid-selection

http://www.swvt.uga.edu/2016/sysr16/AP103-8-sr-resist.pdf

Sugarcane aphids populate under grain sorghum

3) Use an insecticide seed treatment – My trials last year found that insecticide seed treatment would limit seedling infestations for 30 – 40 days after planting.   All registered neonicotinoid insecticides are effective including thiamethoxam (Cruiser), clothianidin (Poncho, NIpsIt Inside) and imidacloprid (Gaucho, others).   Most grain sorghum seed was treated with one of these seed treatments in 2017.

4) Scout early and often – Fields can quickly be inspected for the presence of aphids by looking are on the underside of leaves.  Once aphids are detected, scout at least once, preferably 2 times per week, because aphid numbers build very quickly.  Shinny lower leaves with honeydew are a clear sign of infestation. 

5) Beneficial insects usually do not control infestations – SCA and their honeydew attract large number of beneficial insect predators such as lady beetles, syrphid fly larvae and lacewings.  A parasitic wasp is present in and caused infested aphids to turn a dark blue-gray color.  No aphid fungal disease has been observed either.  Generally the rapid rate of increase in aphid populations overwhelms the beneficial insects and severe plant damage usually occurs. 

6) Treat when aphids reach threshold levels – The current threshold is 50 or more aphids per leaf on 25% pf plants preboot stage through dough stage.  Once threshold is reach do not delay application because infestations can very quickly go from the threshold level to 100% infested plants and hundreds of aphids per leaf.  

7) Use an effective insecticide – PYRETHROID INSECTICIDES ARE NOT EFFECTIVE and may flare infestations by killing all the aphid predators.  Regardless of the insecticide, rapidly expanding populations are difficult to control.  Foliar insecticide options for SCA in Georgia are:

  • Sivanto Prime (Bayer Crop Protection). Sivanto prime has a full section 3 label and a supplemental 2ee label for lower rates on sorghum and other grain crops. The 2ee rates are 4 – 7 fl. oz per acre. Sivanto was very effective in my trials at rates of 4 to 7 fl. oz. per acre with Control usually lasting 21 days or more. At the 4 oz rate it can be applied up to 7 times during the season but has a 21 day PHI.
  • Transform WG (Dow AgroSciences). Transform WG federal label was re-instated last year but sorghum is not on the full federal label. But Transform WG has an approved Section 18 emergency exception for use on sorghum in Georgia in 2017 but the label has not been issued yet. The label will allow for 2 applications per season and not more than 3 oz per acre per crop and has a 14 day PHI. Transform cannot be used during bloom to protect pollinators. In my insecticide trails last season, rates of 1.0 and 1.5 oz per acre were effective. Use the 1.5 oz rate if aphid populations are increasing rapidly.
  • Chlopyrifos (Lorsban Advanced, Nufos, other).   Chlopyrifos is labeled at 1 to 2 pints per acre. The 2 pint rate has a 60 day harvest interval. The 1 pint has a 30 day harvest interval, but is usually not effective. The 2 pint rate was 60-90% control for about 10-14 days. At the 2 pint rate it cannot be used after the boot stage due the 60 day PHI. DO NOT USE CHLORPYRIFOS ON SWEET SORGHUM.
  • Dimethoate ( Dimethoate, Cygon). Not recommended. In my trials dimethoate is variable in control and control if it occurs is only for a week or so.  

8) Good coverage is key to effective control.  Use tips and GPA for maximum coverage especially lower in the canopy. A minimum of 10 gpa by ground and 5 gpa by air is highly recommended.

9) Avoid pyrethroid insecticides for other sorghum pests.   For sorghum midge try to avoid routine pyrethroid sprays for sorghum midge.  Instead scout and treat at 1 adult per panicle.  Chlorpyrifos (1 pint per are) for low to moderate infestations.   If pyrethroids are used they can be tank mixed with Sivanto (Do not use Transform during bloom). Early plantings often avoid serious midge infestations.  For fall armyworm in the whorl, the threshold is 50% infested whorls.  Use Belt, Prevathon or Lannate which are specific to caterpillars.  For headworms, corn earworms fall armyworm, sorghum webworm, the threshold is 1 worm per head and use Belt, Prevathon, Beseige or Lannate.

10) Check fields 2-3 weeks before harvest for infestations.   A treatment may be needed if large numbers are in the head to prevent damage to combines.  Hybrids with taller stalks and more space between the grain and upper leaves may make harvest easier by reducing the amount of leaf material going through the combine.  Large infestation producing large amounts of honeydew and sooty mold may interfere with harvest desiccants.  Transform WG can be applied up to 14 days before harvest.  

11) Silage/forage sorghum control. No work was done specifically on SCA control in silage/forage sorghum.   So the same recommendations for grain sorghum also apply to silage and forage sorghum.   Both Sivanto prime and Transform can be used on silage and forage type sorghums.   Grazing / hay interval is 7 days for both products.  Chlorpyrifos at 2 pints per acre has a 60 day grazing forage, hay interval so is usually not an option for forage and hay sorghum.  In forage/hay types, the later cutting were damaged last year.  Spray coverage is difficult when plants get tall.  If aphids are present but below threshold consider a spray application as late as possible before the crop gets too tall.

12) Sweet sorghum. Sivanto prime, Transform and chlorpyrifos cannot be used on sweet sorghum. There currently are no effective treatment options for sweet sorghum. A section 18 request for use of Sivanto prime on sweet sorghum has been submitted to Us-EPA but the request is still pending.

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Filed under Entomology, Grain Sorghum

Thrips Infestation Predictor For Cotton

At our cotton meeting, UGA Extension Entomologist Dr. Phillip Roberts talked about a new model to help predict thrips infestation. The Thrips Infestation Predictor for Cotton tool can be found at http://climate.ncsu.edu/cottonthripsrisk/ . Dr. Roberts has this to say about the model and scouting:

Thrips are the most consistent insect pest of cotton in Georgia and the southeast.  Near 100 percent of the cotton planted in Georgia will be infested by thrips each year.  Preventive insecticides applied as a seed treatment and/or infurrow application at planting for thrips control provide consistent yield responses.  In some situations supplemental foliar insecticides may be needed in addition to preventive treatments at planting. 

Plant injury from thrips is a function of thrips pressure and seedling growth.  The Thrips Infestation Predictor for Cotton (TIP) tool uses planting date, temperature, precipitation, and knowledge of when and how intense thrips infestations will be to predict risk of thrips injury to cotton.  The TIP model can be used to identify planting dates which are at greatest risk for thrips injury.  The TIP tool will give the best predictions within 10-14 days after you use it, so use at multiple times during the planting and thrips management season would be beneficial.  Dr. George Kennedy has prepared the webinar “Thrips Infestation Predictor for Cotton: An Online Tool for Informed Thrips Managment”.  The webinar includes an overview and how to use the TIP tool and can be found at http://www.plantmanagementnetwork.org/edcenter/seminars/cotton/ThripsInfestationPredictor/

High risk planting dates will require more aggressive thrips management compared with low risk planting dates to achieve acceptable thrips control.  Management options for high risk planting dates would include the use of infurrow liquid insecticides such as acephate, imidacloprid, or aldicarb or the use of a neonicotinoid seed treatment plus a supplemental foliar application at the 1-leaf stage.  In low thrips risk environments neonicotinoid seed treatments will generally provide acceptable control.  The TIP tool should allow proactive decisions to be made relative to thrips managment.

How confident should I be using this TIP tool?  My thoughts are exactly as those of my colleague at NC State who answered this question very well.  Any forecast will have some uncertianty.  However, this tool is based on many years of data from across the Southeast US Cotton Belt and has been validated several years since.  We are very confident that this tool, when used as instructed, will accurately forecast thrips risk in cotton.

The TIP tool will not replace scouting and sampling for thrips and thrips injury in cotton.  But it does provide information which will improve our thrips management programs.

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