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Downy Mildew Disease

Published on 06/04/19

Georgia vegetable growers need to apply fungicides to stay ahead of downy mildew disease.

By Clint Thompson for CAES News

Georgia vegetable farmers should be on alert as downy mildew disease has been spotted in at least three southern Georgia counties this spring. Additional counties could follow as weather conditions remain favorable for the disease into early June, according to University of Georgia Cooperative Extension plant pathologist Bhabesh Dutta.

Cucurbit crops — like cucumbers, melons, squashes and pumpkins — are susceptible to the disease. Dutta ranks downy mildew among the top diseases in cucurbit crops, along with Fusarium wilt and Phytophthora fruit rot.

Downy mildew disease can destroy plant foliage and cause the leaves to curl and die. Without healthy leaves and vines, a plant is vulnerable to blisters and sunscald during hot days, conditions most of Georgia has experienced since early May.

Much of the state has not experienced a substantial rainfall event since the weekend of May 11, and many growers have had no relief from temperatures that reached or eclipsed 100 degrees Fahrenheit.

“We really need some balanced days, not full-blown sunshine with 100 degrees Fahrenheit every day like we’ve experienced here recently, and also not heavy dew nights,” Dutta said. “We need some cloudy days, but most importantly, we need some rain.”

High temperatures during the day, followed by dew at night and in the early morning hours for the past three weeks, have led to the disease developing in cucurbit fields in Crisp, Decatur and Lowndes counties.

“Most of our growers are doing preventative sprays for downy mildew. We do have fairly effective fungicides that can manage downy mildew. I think growers are diligently following UGA recommendations and they should continue to do so,” Dutta said.

Growers need to be aware of what downy mildew symptoms look like and the damage it can inflict on vegetable crops. The pathogen thrives in wet, humid conditions and needs moisture on the surface of the plant for successful spore germination and further infection.

The pathogen that causes downy mildew can’t survive a hard frost, so it overwinters in frost-free regions like southern Florida. During May and early June, wind currents blow the spores into Georgia.

For up-to-date information about potential diseases impacting Georgia’s vegetable production, see https://site.caes.uga.edu/vegpath.

Clint Thompson is a news editor with the University of Georgia College of Agricultural and Environmental Sciences based in Tifton.

Turf Grass News

Turfgrass Blog: 2019 Edition

Clint Waltz, Ph.D.

University of Georgia Turfgrass Specialist

June 10, 2019

 

With the recent dry weather encouraging the use, and possible overuse, of irrigation systems then the recent tropical conditions – rainfall and humidity – I have had several pictures and questions about a jelly-like substance growing in the turf.  The jelly-like “stuff” is a Nostoc algae, a genus of cyanobacterium formerly classified as blue-green algae.  It has multiple common names like star jelly, witch’s butter, and others.  Under warm temperatures Nostoc may appear suddenly in lawns, and other turf areas, following a period of rain and can be an indication of overwatering.  In turf, it is generally on a site where the grass is growing poorly due to severe compaction, overwatering, or both.  It does not cause turf decline or death; it colonizes areas where it has favorable growing conditions and the grass was already thin.  Poor drainage and compacted soils create a favorable environment for Nostoc.  It will dry-out if the water or rainfall diminishes but it has only gone into dormancy.  With enough moisture, it will come back to “life”.

 

In its hydrated, gelatinous, green state it can be a safety hazard.  It is slippery.  Be careful walking on it.  However, when it dries-out it can become restrictive to turfgrass growth.  Nostoc dries into a black crust that can prevent stolons from rooting, or “tacking”, into the soil, delaying turfgrass growth and spread.

 

Nostoc can be difficult to control.  To discourage its growth, encourage the growth of the grass.  Algae is less of an issue with an actively growing turfgrass canopy.  The first step is to check the irrigation system to make sure it is watering properly (i.e. not too regular or too much).  The turfgrass species we grow in Georgia perform better when grown on the slightly dry side, so scaling back the irrigation and adjusting the irrigation schedule will benefit the grass and can discourage the algae.

 

Improve internal soil and surface drainage.  Core aeration opens the soil, allows oxygen into the root system, and reduces compaction.  While allowing the soil surface to dry-out then breaking up the Nostoc “crust” by scarifying the upper ¼- to ½-inch can break the algae into pieces and encourage its spread, it also permits the turfgrass stolons to root into thin areas and outcompete the Nostoc.  With proper irrigation and core aerification the grass can cover and eventually predominate the area where the Nostoc was present.

Clint

 

Summer Heat

Published on 05/23/19

Spring season brings summer heat to Georgia

By Clint Thompson for CAES News

Georgia temperatures are rising, and the weather is only going to get hotter with little rain in the forecast. That’s not good news for Georgia’s cotton producers who are in the middle of planting this year’s crop, says Jared Whitaker, University of Georgia Cooperative Extension cotton agronomist.

According to the UGA Weather Network at www.georgiaweather.net, temperatures eclipsed 90 degrees Fahrenheit in most of south Georgia this past weekend and are expected to reach 100 F by the middle of next week.

“Cotton is going to be the most sensitive crop to these types of conditions just because of the relatively poor vigor of cotton seedlings compared to other crops Georgia producers plant,” Whitaker said. “Cotton seed is very small and conditions need to be near perfect for several days after planting to ensure we get a suitable stand. When soils dry and temperatures rise, it becomes increasingly difficult for producers, especially in nonirrigated fields.”

Whitaker says that an informal survey he conducted last week revealed that around 50% of the state’s farmable fields had been planted. Progress was a little further along than usual because of good planting conditions in late April. Also, producers are trying to minimize their risk from losses that could occur at harvest by planting some cotton earlier than usual.

He is concerned that poor conditions could delay planting to the point that yields are affected.

“We really need to have a good stand established before the end of the first week of June to ensure that we have enough time to make an entire crop,” Whitaker said. Growers need rainfall within the next couple of weeks to get this crop started in the right direction.

“We’re always a week away from a drought,” Whitaker said. “And that’s certainly the case this year.”

The last substantial rainfall was recorded during the weekend of May 10 through May 12. Three days of rain yielded 1.5 inches in Tifton, Georgia; 0.81 inches in Alma, Georgia; 1.2 inches in Griffin, Georgia; and 1.52 inches in Vienna, Georgia.

But since much of the state’s crops are grown in south Georgia’s sandy soils, any moisture that region receives is soaked up quickly.

UGA Extension peanut agronomist Scott Monfort says that approximately 65% of Georgia’s peanut crop has been planted. But like the state’s cotton farmers, Georgia’s peanut producers will need to monitor their crop’swater needs during this extremely hot and dry period.

“To have high temperatures this early is pretty tough. It means these plants are going to go through heat stress earlier than normal this year and farmers are going to have stay on top of it as far as irrigating,” Monfort said. “While we normally wouldn’t irrigate this early, we might have to start if we lose too much moisture.”

Growers also need to be careful planting in fields with marginal moisture.

Summer doesn’t officially begin until June 21. Pam Knox, UGA Extension agricultural climatologist, believes that temperatures in June, July and August will depend largely on how much rainfall Georgia gets.

“There is not much correlation between early season heat waves and the rest of the summer. However, if it stays dry, then hotter-than-normal conditions are likelier just because all of the sun’s heat goes to warming the air instead of evaporating water from the soil and plants,” she said.

For more information about what weather to expect this summer, read Knox’s climate outlook on her blog at https://t.uga.edu/4YB.

Clint Thompson is a news editor with the University of Georgia College of Agricultural and Environmental Sciences based in Tifton.

Root-Knot Nematodes

Published on 05/27/19

UGA survey finds root-knot nematodes in 60% of vegetable fields

By Bryce Ethridge for CAES News

A recent University of Georgia Cooperative Extension survey of 431 Georgia vegetable fields found that more than 60% contained root-knot nematodes, tiny parasitic worms that feed on roots and destroy plants.

The survey was conducted May through December of 2018 by UGA Extension nematologist Abolfazl Hajihassani. His research group surveyed fields in 30 Georgia counties for plant-parasitic nematodes and found 10 genera of nematodes. Root-knot nematodes are the most important nematodes that vegetables producers should be concerned with, he said.

Hajihassani conducted the survey to better understand the incidence, abundance and spread of plant-parasitic nematodes within vegetable fields in southern Georgia. The counties surveyed represent about 85-90% of the state’s vegetable production.

During the survey, soil samples were collected from vegetable fields and nematodes were extracted and identified to the genus level.

“Right now, the root-knot nematode is the main problem in most vegetable crops grown here, based on distribution, soil population density and incidence,” he said. “Therefore, root-knot nematodes will be the target of our future research, which will include the evaluation of old and newly introduced fumigant and nonfumigant nematicides.”

Root-knot nematodes can enter the plant’s roots and move through the cells where they grow, produce more eggs in only three to four weeks and cause the roots to swell. This reduces the plant’s growth and yield potential.

South Georgia’s sandy soils allow nematodes to reproduce frequently because they can move easily through the soil’s loose texture.

UGA Extension’s observations in the field indicated that fumigating the soil before applying plastic will stop the nematodes for the season, but only for that season.

Hajihassani said that there are a few nematode-resistant vegetable varieties available, but Georgia producers don’t want to use them because of quality issues. Growers prefer to plant high-yielding varieties and use chemical nematicides, although they’re not always 100% effective.

Currently, Hajihassani is researching the nine other types of nematodes the survey identified in case they could become threats to vegetable production in Georgia. This includes stubby root, ring, spiral, root lesion, reniform, lance, cyst, stunt, and dagger nematodes.

“Hopefully, in one to two years, we’ll have a good source of information as to what species of nematode we have,” he said. “Through Extension agents, we have already communicated the survey data with those growers who participated in our survey. Our aim is to continue sharing the data with growers, find out what problems they have and design the appropriate management techniques.”

Nematodes need three components to thrive: water, high temperatures and a suitable host. Georgia has water, hot summers and a variety of host plants, which has Georgia farmers concerned. Along with vegetables, nematodes can cause problems in cotton, peanut and tobacco plants.

For more information on Hajihassani’s work and plant-parasitic nematodes, visit https://t.uga.edu/4YK.

Cabbage Crops Signs of Disease

Published on 05/08/19

Farmers must watch cabbage crops closely for signs of disease

By Bryce Ethridge for CAES News

As temperatures increase this spring, Georgia cabbage farmers should scout their crops regularly to ensure that disease pressure is not too high, says University of Georgia Cooperative Extension vegetable specialist Andre da Silva.

If farmers are proactive and maintain proper pest management programs during the growing season, diseases like black rot and Alternaria leaf blight can be controlled, da Silva added.

Symptoms of these disease are easy to identify in the field, but once identified, yield may have already been compromised. The increase in temperatures and rainfall can create perfect conditions for disease, and da Silva and Bhabesh Dutta, UGA Extension vegetable disease specialist, are currently tracking the emergence of the two diseases throughout south Georgia.

“As we get to the summer — or later in the spring — the warmer temperatures increase the chance of these diseases,” he said. “If growers don’t pay attention and keep a proper pest management program, we might suffer a high loss.”

According to the UGA Center for Agribusiness and Economic Development, the farm gate value for cabbage in Georgia in 2017 was $53.6 million.

Alternaria leaf blight can cause spots on some brassica crops and render them unmarketable. Symptoms first appear on older leaves as small, dark spots that gradually enlarge with concentric rings. As the disease gets worse, younger leaves become infected. Infection becomes more problematic in humid and wet conditions.

Black rot causes v-shaped lesions on leaf edges which can lead to the plant’s death.

Lack of proper irrigation scheduling could also lead to the appearance of these diseases, particularly due to the application of high volumes of water.

“Since we’re starting to have warmer conditions with frequent rain showers, soil might have plenty of moisture to supply crop demand,” da Silva said. “There is no need to overirrigate, and if growers are irrigating their cabbage in those conditions, it’d create the perfect conditions for disease. That’s what we don’t want.”

As part of his research on the UGA Tifton campus, da Silva is looking for cabbage varieties that are more disease tolerant or disease resistant.

Until disease-resistant varieties are discovered, growers should keep these tips in mind when managing diseases in cabbage:

  • Maintain a proper pest management program.
  • Rotate chemical products to avoid disease resistance to a particular product.
  • Change up irrigation schedules to apply water only when necessary.
  • Frequently survey crops for symptoms.

To learn how to identify rot, contact da Silva at 229386-3806 or adasilva@uga.edu. For more information on the Department of Horticulture at UGA-Tifton, visit http://tifton.caes.uga.edu/departments/horticulture.htm

Some Georgia Lawns “Greening Up” Faster Than Others

While many warm-season turfgrass species have shown signs of significant green-up, some grasses and locations still have an appearance of being dormant or slowly transitioning.

To date, the average 4-inch soil temperature for the entire month of April on the University of Georgia campus in Griffin, Georgia — fairly central for the state — is 64.1 degrees Fahrenheit. In general, this is warm enough to get green growth, but it is barely warm enough to stimulate root growth or initiate new growth from rhizomes buried within the upper couple inches of the soil for Bermuda grass and zoysia grass.

Understanding the growth characteristics of Georgia’s warm-season species and considering recent environmental factors, it is not surprising that most grasses appear green while others seem slow to green up. The “slower” grasses, or locations within the landscape, could be delayed by other influences.

If grass is growing in an area on the north side of a building, in a low area that retains more water, in a wet spot in the landscape, where the ground is shaded or geographically north of Griffin, it may be a little slower to green up. Water is a good buffer of heat, meaning that it takes more of the sun’s energy to warm the soil to the same temperature than if the soil were dry. Wet areas will green up more slowly than drier areas.

Considering the amount of rain the state has received since last summer, all Georgia soils likely have good to excellent moisture content. Also, a thin area may be slower to cover, or appear green, because the soil temperatures for initiating new shoots from rhizomes will take more time. It takes more time for warmth to move through the soil and trigger new growth than it takes for the new shoot to reach the soil surface.

Warm-season grasses have changed substantially over the past two to three weeks. Likewise, the next two to three weeks should encourage growth and green-up.

They say “patience is a virtue,” and a little green grass seems to cause us to be less virtuous. Be patient and stay with the program. Georgia’s warm-season turfgrass species should be growing strong shortly.

For more turfgrass information from UGA Cooperative Extension, go to www.georgiaturf.com.

Clint Waltz is a Cooperative Extension turf specialist with the University of Georgia College of Agricultural and Environmental Sciences.

Valor on Peanuts

Valor Mishaps (Prostko)

In the heat of the battle to get crops planted on time, it is not uncommon for some herbicide misapplications to occur.  The unintentional application of higher than labeled rates is a not a good thing because money is wasted, crop injury potential is increased, and rotational crop intervals are jeopardized.  

Over the last few days, I have received several inquires about how peanuts might respond to Valor applied at rates higher than 3.0 oz/A due to sprayer calibration errors.  Keep in mind that when an herbicide is developed, application rates are based upon a ton of data.  The lowest use rate possible that will provide the most consistent weed control over a wide range of environments in carefully selected.  Additionally, most herbicide use rates have a “safety” margin built into the rate just in case of application errors.  

I looked back at some of my older Valor data and can tell you this regarding the response of peanuts to 6 oz/A of Valor:

1) In 6 field trials, there was no significant difference in peanut yield between 3 oz/A and 6 oz/A.

2) In 1 field trial, 6 oz/A of Valor resulted in a 7% yield loss when compared to 3 oz/A (Figure 1).

3) In 1 field trial, 6 oz/A of Valor resulted in a 15% yield loss when compared to a non-treated check.

Figure 1.  Peanut injury caused by Valor SX 51WG @ 6 oz/A which 
resulted in a 7% yield loss, Attapulgus, GA 2018.  


If a grower accidentally applied the wrong rate of Valor at planting, there is a good chance that nothing disastrous will happen.  With any application of Valor and regardless of rate, heavy rainfalls during the period of emergence until about 2-3 weeks after will result in significant visual injury.  I strongly encourage all growers to regularly calibrate their sprayers in order to prevent herbicide application mishaps!  Growers should not put all their faith in last year’s sprayer settings or sophisticated on-board computers.  

For the record, both UGA and the current Valor label recommend that ONLY 3 oz/A of Valor be applied within 2 days after peanut planting (I do not want anyone reading this blog to think that its OK to apply 6 oz/A!!!!!!!!!  That is not the purpose of this blog!!!!!!!).  V

New Extension Publication on Herbicide Injury of Pecan

Volunteer Peanut Control in Field Corn

Volunteer Peanut Control in Field Corn (Prostko)

Been getting a few calls about controlling volunteer peanuts in field corn.  Remember that the volunteer peanuts that emerge from seeds that made it thru the winter and rains are some super tough plants.  A couple of thoughts:

Roundup Ready Corn:  Split applications of glyphosate at least 10 days apart.  Glyphosate can be applied over-the-top of field corn up to V8 stage or 30″ whichever comes first.  Drop nozzles or lay-by applicator should be used when corn is 30″ to 48″ tall.

Liberty-Link Corn: Split applications of Liberty (glufosinate) at least 7 days apart.  Liberty can be applied over-the-top up to V6 stage of growth.  For corn 24″ to 36″ tall, apply with drop nozzles or lay-by rig.

Conventional Corn:  Split applications of dicamba @ 0.25 lb ae/A applied EPOST (8″ tall corn) + lay-by (up to 36″ tall corn).  These dicamba applications must be separated by at least 14 days.   An alternative treatment would be dicamba (EPOST) followed by Evik (lay-by).

**Atrazine can also be included in any of these EPOST applications as long as corn is < 12″ tall.

Strongarm/Peanut Questions

Strongarm/Peanut Questions (Prostko)

Had a few questions about Strongarm (diclosulam) use in peanuts yesterday that I thought might be interesting to all:

1) In general, what application method is more effective for weed control in peanut (PPI or PRE)?

When averaged over 7 weed species, there was little difference in weed control between PPI and PRE applications of Strongarm (Table 1).  However, in dryland production fields with minimal future rain predictions, PPI applications would be preferred.

Table 1. Application Method Effects on Residual Weed Control with Strongarm 84WG @ 0.45 oz/A in Peanut.1

Weed Control (%)
Application Method
PPI2 PRE3
sicklepod 54 44
Florida beggarweed 78 87
bristly starbur 94 97
purple nutsedge 59 73
yellow nutsedge 78 78
morningglory sp. (Ipomoea sp.) 89 99
smallflower morningglory 94 96
All (average) 78 82

1Source: Grey et al.  2003.  Peanut Science 30:27-34.

2PPI = preplant incorporated.

3PRE = preemergence.

Also very important to remember that Strongarm provides a much broader spectrum of weed control when applied PPI or PRE when compared to POST applications.  However, the following 7 weeds are sensitive to Strongarm when applied POST: tropical spiderwort/Benghal dayflower; common cocklebur; common ragweed; bristly starbur; horseweed/marestail; morningglory sp.; and eclipta.

2) What application method is more effective for the control of tropical spiderwort/Benghal dayflower?

Data collected a few years ago in Grady Co. indicated that POST applications were more effective than PRE applications for the control of tropical spiderwort/Benghal dayflower (Table 2).

Table 2. Application Method Effects of Strongarm 84WG @ 0.45 oz/A on Benghal Dayflower/Tropical Spiderwort Control in Peanut.1

Application

Method

Control (%)2
46 DAP3 69 DAP 114 DAP
PRE4 75 cd 68 b 11 e
EPOST5 97 a 90 a 75 abc
LPOST6 88 ab 78 ab 60 c

1Source: E.P. Prostko and J.T. Flanders, 2003, PE-24-03, Unpublished data.

2Means in the same column with the same letter are not significantly different according to DMRT (P=0.05).

3DAP = days after planting.

4PRE = preemergence.

5EPOST = early-postemergence, 17 days after planting (2’’ tall, 3 leaf stage).

6LPOST = late-postemergence, 31 days after planting (6” tall).