Monthly Archives: August 2016

August Peanut Insect Update

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This is kind of been a cotton week for me; I haven’t looked at many peanuts this week. Here’s a field I was going to pop in and scout for disease until I saw this water. I’m tired of losing my boots in these kinds of fields.

UGA Entomologist Dr. Mark Abney wrote an insect update I’ll pass along for everyone:

Drs. Monfort, Srinivasan, and I spent several days last week walking peanut fields to get a measure of how severe tomato spotted wilt is in this year’s crop. Incidence of virus symptoms varied from 0 to over 30% in the fields that were surveyed. This effort also gave me an opportunity to see first hand what else was happening in terms of insect and mite activity over a large area of South Georgia. As a general rule, insect pressure was low, but there were a few fields with real or developing problems.

Redneck Peanut Worm & Lesser Cornstalk Borer

Several non-irrigated fields had lesser cornstalk borer infestations, and a couple fields had two spotted spider mites. Redneck peanutworm was the most common foliage feeder I saw. This insect has been very abundant in my test plots this year. I thought the redneck peanutworms had run their course a week or so ago, but we seem to have another generation showing up on the research farms around Tifton. There are no thresholds for this insect, and I doubt that it will cause measurable yield loss in most situations. It does however, make the foliage look ragged.

Southern Corn Rootworm

Southern Corn Rootworm - Adult - Dr. Mark Abney

Southern Corn Rootworm – Adult – Dr. Mark Abney

Some fields had relatively high numbers of southern corn rootworm (cucumber beetle) adults, and I received a couple more reports of pod damage this week. As I mentioned in a post last week, there is little that can be done to manage rootworm infestations in peanut once the larvae are feeding on pods.

Caterpillars

I have not seen much in the way of caterpillar pressure, but I have gotten calls that indicate some fields are experiencing moderate to heavy infestations. There are velvetbean caterpillars, soybean loopers, and armyworms in spots. Most of the moths I saw in fields last week were tobacco budworm. I will be watching my plots closely for caterpillars in the coming weeks.

Whiteflies

Whiteflies are not typically a pest of peanut, but we are seeing some whitefly activity in peanut fields in Tift and surrounding counties. So far, there have been no reports of reproduction occurring in peanut, and we should all hope that does not change. There are few options available for whitefly management in peanut, and most fields still have a long way to go before harvest. If anyone observes whitefly nymphs on peanut, please let me know.

Garden Fleahopper

Garden Fleahopper

Garden Fleahopper

Folks are seeing garden fleahopper in peanut again this year. The impact of this insect on peanut is unknown, but some fields were treated in 2015 due to very high populations and subsequent defoliation. We do not have a good option for controlling garden fleahopper; pyrethroids have generally provided only partial control.

Growers should be aware that there is a “little bit of everything” in terms of insect and mite pressure in Georgia peanut fields right now, but that does not mean every field is infested or will need to be treated.

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Filed under Entomology, Peanuts

Silverleaf Whiteflies

I was in cotton yesterday checking for disease and saw a few whiteflies. There were not many, so I don’t think we should be concerned bad. This was in Meigs. Usually, we see whiteflies in Pavo. This is because of the vegetable production from Colquitt County that is closer to us.

If you see whiteflies, check under the 5th leaf for immatures. They look like little lemons. I have a picture of what bad whitefly populations look like under a soybean leaf. If you find whiteflies you should avoid using dicrotophos alone (Bidrin or others) or limit its use for stink bugs, as it could allow whiteflies to flare.

Adult whitefly

Adult whitefly

The following is the method to check for whiteflies thanks to Irwin County Agent Phillip Edwards:

1) Count down from the terminal of the plant to the fifth vegetative leaf (starting with any leaf that is the size of a quarter or bigger).

2) Slowly turn the 5th leaf over to view the underside of the leaf.

3) See if there are any immature whiteflies present. If 50% or more of the 5th leaves checked have multiple immatures on them, then treatments should be started.

Immature Silverleaf Whiteflies

Immature Silverleaf Whiteflies

Insect growth regulators like Knack or Courier can be used if the population is not too high. These options are slow acting, and results are not seen until 5 to 7 days after treatment. If populations have already exploded, then other insecticide options may be needed.

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Filed under Cotton, Entomology

Pond Weeds: Duckweed & Watermeal

Duckweed-Watermeal 013

I’ve had fewer pond weed calls this year of any. I was talking with Alan Dennard this morning, and he has noticed the same. Last week, I was asked about algae in a pond. Sometimes these small, floating weeds resemble algae from the road. But this is actually duckweed mixed with watermeal. Both of these weeds are commonly seen together. In the morning, they will cover the entire pond. By afternoon, they float around pushed by wind. Oxygen depletion becomes an issue once these weeds take over a pond. There were no fish in this pond, but if this was eliminated all at once, we’d likely see a fish kill. Both of these weeds tend to grow in quiet, undisturbed water.

Identification

There are different chemical recommendations for each of these weeds; however, there are also compounds that will kill both however. Both are seed bearing plants, but duckweed is separated from watermeal by its roots. Duckweed has 1 to 3 leaves or fronds with a single root hair coming down. Below is a more up close photo:

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Duckweed is larger than watermeal

The microscope picture below shows the difference in size between duckweed and watermeal.

Watermeal & Duckweed

Watermeal & Duckweed

Control

We would absolutely need to kill only 1/3 of this at a time (if fish are present). Diquat (Reward) has activity on both weeds, as also does Clipper and Sonar.

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2016 PGR Management, Cotton Varieties, & Rainfast

If I haven’t looked at cotton elsewhere, we’re watching our variety trail which was planted in late May. So, we’re putting on plant growth regulators now, but most folks have been started for a while. It’s definitely getting late to discuss this now, but there may be some points here that can help us make some decisions.

One of the biggest factors in PGR’s is variety. Below is the updated variety considerations from the 2016 UGA Cotton Production Guide. It’s good to know what varieties have lots of growth potential. Slower growering, earlier maturing varieites may not need aggressive PGRs (high rates, prebloom applications).

2016CottonPGRs

There’s a lot of good info in the 2016 UGA Cotton Production Guide. I’ve taken some points, but is worth a read on that link if you got time.

Irrigated

In most irrigated fields, Dr. Whitaker says we can confortably being low rate applications (4oz) at least by the second week of squaring and continue on a 14 day interval for three or four applications. Another approach is to apply 8 – 12 ounces at first bloom or before with a subseuqnt treatint two to three weeks later at same rate. The key for aggressive varieties may be making applications earlier, when the plant is 12 to 16 inches tall, especially in fields that frequently receive or retain moisture.

Dryland

In dryland situations, applications at or just prior to first bloom is usually a time to consider mepiquat at rates near 8 oz if growth is vigorous. If aggressive growth continues, a follow up treatment may be needed.

When is too late?

It’s important to remember that a given rate of mepiquat in a small plant has more effect than the same rate in a large plant. This has to do with concentration. Dr. Whitaker says, if we are trying for a single application program, we should target cotton in the 16 to 24 inch range. Applications not made until cotton reaches 30 inches often do not adequately control growth. If we feel like we’ve passed the 8 ball here, instead of a high rate, Dr. Whitaker has seen the best response from 1 pint of mepiquat followed by another 1 pint NO LATER than 10 days apart.

Rainfast

In 2013, we could hardly get a PGR application without rain coming in right behind it. We’ll have the same issue this week with our tropical storm thing coming through. Make sure to check each label for specific information, but here are some general guidelines:

Rainfast

 

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Bacterial Blight In Cotton

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We are seeing bacterial or angular blight again in cotton. I have a dryland variety trial I looked at this morning and it is showing up in different varieties. Unfortunately, we cannot do anything we can spray. We can irrigate during the night to reduce leaf wetness. Our trail was planted in late May, so we are being everything else. Cotton is not yet too rank. I’m not seeing but a few leaves here and there, but every leaf I find has already dropped from the plant. It is too early to know how much this will impact us. Here is more information from UGA Extension Pathologist Dr. Bob Kemerait:

Once again, we are finding bacterial blight, caused by Xanthomonas citri pv malvacearum, in cotton in Georgia.  The disease can be diagnosed by presence of water-soaked-to-necrotic spots on the leaves that are delimited by the veins of the leaf. This gives the spots a particular “angular” appearance.  The disease can also spread in the veins and gives a “lightning bolt” streak on the leaf.  Crater-like, water soaked lesions can form on bolls.

There is nothing that can be done to manage this disease.  Managing growth of the crop and irrigating at night to reduce leaf wetness periods can help a little. 

Photo by Jeremy Kichler

Photo by Jeremy Kichler

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Filed under Cotton, Disease

Dollar Spot In Bermuda Pasture

Tift85-Hay

Last week, I mentioned seeing leaf spot in the pasture. UGA Extension Pathologist Dr. Alfredo Martinez wanted to confirm what appeared to be fungal structures on the leaves as well. The last few years, we’ve looked at leaf spot pathogens in hay fields. Usually, it is leaf blight (Helminthosporium) or leaf rust. What we looked at a few weeks ago appeared to be more damaging to the lower leaves. The lesions of dollar spot are white to straw colored surrounded by a brown border. This was affecting the lower leaves bad. This is the first time I’ve seen dollar spot in pasture. It is maintained the same as helminthosporium and/or leaf rust. Keep in mind, this pasture was burned off last season.

Dollar Spot

Dollar Spot

Looking at the pasture, Tim Flanders noticed these odd structures on the leaves. They almost looked like a fertilizer granular. Dr. Martinez plated them out and did find them to be fungal related. There were basically some saprophytic fungi that ARE NOT associated with the dollar spot.

Dollar Spot lesions

Dollar Spot lesions

Management

Management is strictly avoidance. Coastal, Tift 44, and Tift 85 have some level of resistance (to leafspot pathogens) while Alicia is extremely susceptible. But even less susceptible varieties are infected with leaf spot when potassium is low. Most reported leaf spot cases are directly related to low soil potash. Nutrients are removed from bermuda hay fields in about a 4-1-3 ratio of N, P2O5, and K2O with harvest. We need 75 percent as much potash as nitrogen  applied each season. Split applications of K are better in sandy soils. It is also advised to remove inoculum that exists in thatch. In addition to tying up nutrients, thatch holds water and reduces air circulation. This is a conducive environment for inoculum. The only practical way to reduce thatch is burning in spring before green-up.

Visit Leafspot Diagnosis and Management in Bermudagrass Forages for more information.

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Filed under Disease, Forages

Fruit Thinning & Irrigation Scheduling

Pecans 007

We’ve had scattered rain so far this season, and nuts are beginning to size. Our scab levels are low thanks to  fungicide sprays and scattered rain. This is the period where our female flower is beginning to set physiologically in the tree, so any stress now is greater impact. There have been reports of aphids, and some growers have sprayed already. Here is some information from UGA Extension Horticulturalist Dr. Lenny Wells on fruit thinning:

Pecans 008For the brave souls willing to thin some nuts from heavily loaded trees, now is about the time for most of our mid-season cultivars. Varieties like ‘Creek’, ‘Stuart’ and ‘Cape Fear’ should be ready as early as (last) weekend and certainly by (this) week for most of south Georgia. See here for a previous post on fruit thinning and how to cut nuts to determine if your crop is ready to thin.

Even though it is hot and dry, if you plan to fruit thin, it is wise to turn off the irrigation a day or two prior to thinning in order to minimize the chances of bark damage to the tree. Also, with the hot, dry weather many growers are anxious to begin running their irrigation at 100% capacity. Bear in mind that we are still in the nut sizing stage on most cultivars with the exception of ‘Pawnee’ and a handful of other very early cultivars. We don’t need to go to full capacity until we enter the kernel-filling stage. If you have a September harvest cultivar like ‘Pawnee’ you should be operating at full capacity now in order to fill the nuts. For most other October harvest cultivars change your irrigation to full capacity about mid-August (another couple of weeks).

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