Leaf Spot & Dry Pastures

Pasture (2)

BermudaLeafSpot-1

Bipolaris Leaf Spot

We were looking at a pasture in Boston last week that was needing to be cut. It turned out it was just really dry in some spots and needing some rain. This pasture is predominately Bahiagrass but also plenty of bermudagrass. Both grass species were showing decline symptoms resulting from drought. On the bermudagrass I could see some leaf spots. The leaf spots on Bermuda are caused by either rust or Helminthosporium fungus. Here is what UGA Extension Pathologist Dr. Alfredo Martinez has to say:

Leaf spot caused by Bipolaris is observed on the leaves of this grass. It is a common disease this time of the year. Low potassium and high nitrogen are usually the culprit in addition to other stresses. Dry soils and wet foliage by dew can be problematic.

Information on leaf spot diagnosis and control is located at Leafspot Diagnosis and Management in Bermudagrass Forages.

Santos-Pasture (3)

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Late Fertility Decisions On Cotton

NexGen-CottonTrial

We’re seeing some fields showing some nutrient issues which have reached 6th week of bloom. The field above had the red tint similar to potash deficiency in which we decided to run a leaf tissue and petiole sample. Everything actually came out good except nitrogen. UGA Extension Fertility Specialist Dr. Glen Harris says we generally do our leaf tissue samples before bloom and petiole following bloom. When one is taken this much after bloom it can be difficult pin pointing issues, especially nitrogen.

We were not much under nitrogen uptake, but was still puzzling since a normal recommendations were applied. We are now at 8th week of bloom, and at this time no foliar applications would economically improve the situation. There is always discussion about waiting on bolls in the upper portion of the plant. Dr. Harris says, “Based on field research trials, foliar fertilization is most effective when applied during peak bloom or the first 4 weeks of bloom. Foliar feeding during the 5th – 7th week of bloom may or may not be effective depending on the particular cotton variety. Once you pass the 8th week of bloom, it is too late and no foliar feeding is recommended.”

It is difficult to determine fertility problems in fields were we rotate in and out each year. In the case where we  are in the same field for subsequent seasons, we can make changes to our fertility program.  increase our total N inputs to prevent the same issue. But even a slight increase or decrease in something like N, we still have to think about how more or less rainfall can affect outcome.

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White Sugarcane Aphids

Sorghum 013

We were looking at sorghum yesterday and saw many, many aphids with a lot of honeydew on the lower leaves. Some sorghum is not producing heads just yet. The aphid turns out to be a new aphid in the state, white sugarcane aphid(Melanaphis sacchari). The initial problems found with these aphids in Texas were discovered during harvest, since the large amount of sticky honeydew produced by aphids choked combines and losing grain. UGA Extension Grain Etnomologist Dr. David Buntin says, “Subsequent reports find the aphid in 9 total counties in the southwest quadrant of the state Marion, Decatur, Early, Seminole, Colquitt, Taylor, Terrell, Randolph, and Tift counties.” (Now Thomas.)

White Sugarcane Aphids 007

Here are some more notes by Dr. Buntin:

“The white sugarcane aphid (WSCA) has occurred in Florida since 1977 and Louisiana since 1989 feeding on sugarcane.  About 2 years ago the aphid shifted its host preference to grain and forage sorghums. First found in Texas, this new strain has rapidly spread eastward across the southern United States in 2014 and is now widespread in Mississippi, Louisiana, and eastern Texas, and Arkansas.  It is expected that WSCA will continue to spread rapidly throughout Georgia over the next few months.  It is important to scout sorghum fields in your area for its presence. It is fairly easy to identify.  Wingless forms are a uniform pale cream to yellow with black feet and black cornicles (the small tubes present on the end of the back).

White Sugar Cane Aphid-2

White Sugar Cane Aphid - Sorghum 005Where it has been found in Georgia, it is present in many fields at very high numbers of several thousand aphids per plant across entire fields. The aphid sucks plant fluid and these large populations are causing injury to the plants including death of leaves and sometimes plants. The aphid remains present in field until harvest. It produces large quantities of honeydew, a sticky sugary substance that adheres to the plants, which may interfere with harvest and may damage combine harvest equipment. Entomologist in Texas, Louisiana and Mississippi report 20 to 50 % yield loss and sometime the total loss of the crop from harvest damage.  A tentative threshold is: treat if more than 30% of plants are infested AND there is an average of 100 – 250 aphids per sorghum leaf.  This publication from Texas AgriLife Extension shows the different aphids on sorghum and information about white sugarcane aphid biology and damage: http://nueces.agrilife.org/files/2014/05/Sugarcane-Aphid-Publication.pdf   Interestingly, a study by Kathy Flanders at Auburn University suggests this new strain prefers sweet, grain and forage sorghum over sugarcane and it does not attack millets.

Adult White Sugarcane Aphid

WSCA is difficult to control and populations may bounce back quickly following an application. Currently labeled insecticides in grain sorghum are not adequate.  High rates of Lorsban (24-32 oz) appear to provide decent control but cannot be used for late-season infestations because of the 60 day preharvest application restriction.  Dimethoate, malathion and the 1-pint rate of chlorpyrifos provide only about 50% control.  Pyrethroid insecticides are not effective and may flare aphids.  If headworms occur, consider using Belt or Prevathon for control.  The states of Texas, Louisiana, Mississippi, Arkansas and Oklahoma have a Section 18 (emergency use exception) exception approval to use Transform WG (sulfoxaflor, Dow AgroSciences).  Studies in these states show an application of 1.0 – 1.5 oz per acre is about 90% effective, although aphids can build back in a few weeks. We are working on a section 18 emergency use exception request for Georgia, but Transform WG is currently not allowed in Georgia.”

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Soybean Caterpillars

Soybeans 002

Don Vick and I looked a quite a few cotton, peanut and soybean fields yesterday. We observed the most insect pressure in soybeans. This field is around R5, beginning seed stage. Walking in the field, it was easily to note the leaf damage. At this growth stage, 15% leaf damage is our threshold. I always like to do a ground cloth sample. If you sit down in the row and shake soybeans, you can count insects per row foot. I also used a sweep net.

This field needed to be treated based on foliage feeding insect thresholds. The caterpillars we were finding were soybean loopers and velvetbean caterpillars. VBC has 4 pair of abdominal prolegs and wiggles when disturbed. We had to check recommendations since soybean looper is resistant to pyrethroids and Steward does not have good activity on VBC. Also, they mixed another fungicide with it for Asian Soybean Rust. Here is an example of threshold for foliage feeders in soybeans:

Foliage Feeder Thresholds Soybeans

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Filed under Entomology, Soybeans

Boll-Feeding Insects

Cotton-002

Cody Weaver and I were checking quite a few cotton fields this morning. At 8th week of bloom, and our stink bug threshold moves into the 50% range since there are so few bolls left stink bugs are likely to damage. The highest damage CottonBollDamage 014we found was 10%. We did see a leaffooted bug which is also a boll- feeding insect. It is in the same insect order, Hemiptera, as stink bug but in the family Coreidae. They also have piercing-sucking mouthparts. UGA Extension Entomologist Dr. Phillip Roberts says we cannot decipher the damage from a stink bug, leaf-footed bug, plant bug, etc. We just check for damaged bolls and include them in our percentage. Here is a damaged boll we found with both lint and warts.

We’re also seeing lots of dropped bolls resulting from drought conditions. There were not has many bolls opening in these fields. We also identified many minute pirate bugs, a beneficial insect. They are easier to see in the blooms since they are small and black colored.

Leaffooted Bug

Leaffooted Bug

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Late Season Peanut Weeds

Peanuts Weeds 010

Some hemp sesbania, sicklepod and pigweed escapes are some weeds we are seeing in peanuts now. Questions coming in about tank mixing with fungicides and non-selective applications. Below is information from UGA Extension Weed Scientist Dr. Eric Prostko:

  1. Can I tank-mix Mn fertilizers with herbicides and/or fungicides? Recent research from NC State University indicated that manganese did not affect the efficacy of Select, Poast, Cadre, Pursuit, 2,4-DB, Abound, Bravo, Headline, or Folicur.  Common ragweed control with Cobra was reduced 6% by dry Mn sulfate but not liquid Mn.   (Peanut Science 2012 39:1-8)
  2. What weeds can be controlled using non-selective applicators (NSA) such as the Weed-Wiper or ropewick? UGA has data to suggest that Palmer amaranth, Florida beggarweed, and sicklepod can be controlled late-season with NSA using a 50% solution of paraquat.  Refer to page 452 of the 2014 UGA Pest Control Handbook for additional information. Remember that the only benefits of this type of application would be improved harvest-efficiency and fungicide spray deposition.  It is way too late to recover any competition related yield losses.
  3. Is there anything that can be done to help control Benghal dayflower/tropical spiderwort at this time of the year (i.e. 100+ day old peanuts)? No. Revenge sprays are not practical. Dayflower/spiderwort plants at this time of the year are too big to control with herbicides.  Additionally, late-season applications of herbicides such as Strongarm could have a significant impact on 2015 crop rotations.  Although Aim can be used as an harvest-aid, previous research has shown that single applications to 8-10″ tall spiderwort plants provided < 45% control.

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Possible Resistance Issues In Curcubit Downy Mildew

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Pumpkins are really difficult to grow here because our disease and insect pressure is so strong at normal planting time. Here are some that have been flowering for a few weeks and first we saw flowers dropping. It turns out that these are male Pumpkins-MaleFlowers-003flowers with the long stems. It blooms for a day. The female flowers have shorter stems and come out usually a week after. With the heat this weekend, likely caused us to lose some flowers. For now, we need to watch for the female flowers and make sure those are not dropping. They have a 1-2 inch stem with a swollen base were pumpkin is forming.

We also have to be aggressive with disease prevention. Here is some early signs of downy mildew. There are some resistance concerns we need to be aware of with downy mildew in curcubits. Here is an update from Hunt Sanders, Disease Management Specialist in UGA Department of Plant Pathology:

“Based on what we are seeing in our cucumber trials this year, we may be experiencing some fungicide resistance problems in downy mildew of cucumber this fall.  Some plots that have been sprayed with a Ranman/ Zampro rotation have a great deal more downy mildew in them than we are used to.  We are using an older cucumber variety in these trials with no downy mildew resistance, but we still should not be seeing the level of disease severity in these plots that we are seeing.  The trial in question is an industry trial with different fungicide rotations which makes it hard to determine which product (Ranman or Zampro) might be experiencing a problem. We have initiated a follow up fungicide screening trial that will help clear up what we are currently seeing. Results from the screening trial should be available in 3-4 weeks.  Until that time all we know is that we are seeing increased levels of downy mildew in plots that were sprayed with a Ranman/Zampro rotation.  I have been in contact with Dr. Langston about current downy mildew recommendations and

Downy Mildew - Pumpkin

Downy Mildew – Pumpkin

we both want to stress how important it is to tank-mix products that contain mancozeb or chlorothalonil with the products Ranman or Zampro.  In the current environment it is critical that your growers tank-mix these products.  If you have a grower that experiences an outbreak of downy mildew that he cannot control with the current fungicide recommendations please contact me and I will investigate the situation.”

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Filed under Disease, Vegetables