Cotton seedling disease returned to west Tennessee fields in 2001

For three years in a row, University of Tennessee plant pathologist Melvin Newman's bosses kept telling him what a good job he was doing educating west Tennessee cotton producers about seedling disease.

The compliments were a bit tongue-in-cheek, however. While losses in cotton due to seedling disease had declined for three years in a row, as Newman's superiors had observed, it was due more to a streak of good weather at planting rather than growers rushing out to purchase fungicides.

In fact, Newman felt that the use of fungicides by growers looking to slash costs, was declining, despite his warnings that seedling disease appears often enough during a five-year period to make an annual fungicide application pay off.

Newman isn't one to say he told you so, but his prognostications have proven to be right on target since 1997 with three years of declining seedling disease pressure sandwiched by two bad years.

“In 1997, we lost 9.5 percent of our crop to seedling disease in west Tennessee,” he says. “In 1998, it was 7 percent, 1999, 5 percent and 2000, 4 percent. In 2001, losses jumped back up to 8.5 percent.”

One thing to consider is that during the three years in which seedling disease in west Tennessee declined, North America was under the influence of the La Niña phase of the El Niño/La Niña weather phenomenon. La Niña produced mostly warm, dry springs in the Delta.

The La Niña finally began to fade in the latter part of 2000, and that brought a return to more normal weather in the spring of 2001. Now weather forecasters are saying the El Niño phase is returning. El Niño, which last appeared in 1997, typically causes wet springs in the Delta, as has been occurring in 2002.

Newman understands the farmers' economic dilemma: Low prices and uncertainty over the farm bill are pushing them to try to lower their cost of production. “They are under an economic crunch. And fungicides are usually the first thing that a farmer will leave off,” he said.

Newman has several suggestions for cost-conscious producers.

“If you're planting early, and in cooler soils and in no-till situations, you need a full-rate of in-furrow fungicides,” he notes. “As the season warms up, you can go to overcoats and hopper box treatments and save a few bucks there.”

Farmers can also reduce their fungicide costs as the season goes on by. “No. 1, you can cut back on Pythium materials like Ridomil Gold as the soil warms up. But I would always keep the Rhizoctonia fighter in there whether it be Terraclor, Quadris or Rovral.”

There's not a lot you can do about another seedling disease common to west Tennessee, Thielaviopsis or root rot. “About the only thing that can help is a Baytan seed treatment.”

Another fungus which attacks cotton, Ascochyta blight, also known as wet weather blight, can be minimized by no-till. In conventional-till cotton, rain can splash the soil-borne spores of the Ascochyta fungus onto the leaves of the plant, causing disease lesions.

Growers should also monitor soil temperature — which has the largest impact on the incidence of seedling disease, according to Newman.

“Remember that soil temperature in no-till is often lower than in conventionally-tilled ground,” Newman said. “We did some temperature checking in no-till corn last week, and where the soil was covered in debris, the soil temperature was 50 degrees. Where it was clear of debris, it was 55 degrees. That's a big difference when you're planting cotton.”

Fungicide Formulation 2Rate/Acre
In-furrow granular fungicides
Terraclor Super X 18.8G 6-10 lbs.
4Terraclor 15G 5.5-10.6 lbs.
Ridomil Gold PC GR 10.5G 7-10 lbs.
Ridomil Gold GR 2.5G 1.25-2.5 lbs.
In-furrow fungicides + insecticides combinations
Terraclor Super X-Di-Syston 6.5G-1.63G-6.5G 12-15 lbs.
1Terraclor Super X + Di-Syston EC 17.5-4.3-17.5 4-5.5 pts. (40-inch row spacing) 5-6.75 fl. oz./1,000 row ft.
In-furrow sprays
Ridomil Gold EC + Terraclor 4EC + 2EC 1-2 ozs. + 3-6 pts.
Ridomil Gold EC + PCNB2-E 4EC + 2EC 1-2 ozs. + 2-4 qts.
3Rovral 4F 3.4-6.9 ozs.
Terraclor Super X 2.5EC 3-6 pts.
Ridomil Gold PC Liquid (Twin Pak) PCNB-24% @ 2 qts./A + Ridomil-47.6% @ 1 oz./A 2 qts. and 6.25 ozs. (1 jug/5 acres)
3Quadris 2.08F 5.2-9.5 ozs.
Hopper-box dusts and slurries (not as effective as in-furrow methods under severe disease conditions)
Delta Coat AD (HB slurry) 3.5% - 30 % 11.75 ozs./100 lbs. seed
Prevail (HB dust) 15%-15%-3.12% 8-16 ozs./100 lbs. seed
NOTES: In-furrow spray treatments are recommended in 3-5 gallons of water per acre. Terraclor Super X or Ridomil Gold PC GR granules can be applied in-furrow with Temik 15G or Di-Syston with a split box method. See pesticide labels for other use instructions and precautionary statements.
1 In-furrow liquid applications: Apply the specified dosage to the soil around the seed and to the covering soil as it fills the furrow. Do not apply directly to the seed. The soil around the seed and the covering soil should be thoroughly mixed with the product. Use the higher rates when weather conditions are expected to be unfavorable for rapid germination and in fields having a history of disease problems or in no-till situations.
2 Dosage rate at 38-inch row spacing.
3 Under cold, wet conditions where Pythium may be a problem, tank-mix with Ridomil Gold 4EC or Terrazole 4EC for added control (see lable for rates).
4 Use where Pythium will not be a major problem.

According to Newman's 2001 research, using an in-furrow fungicide will pay off in west Tennessee. “Where we used an in-furrow fungicide in our lower Brownsville Road plots, we increased yields an average of 118 pounds per acre over not using an in-furrow at all.”

At 50 cents a pound for cotton, that's a $59 per acre increase. An in-furrow fungicide costs $10 to $12 per acre.

In the three years prior to 2001, when weather conditions were not as conducive to seedling disease, “you likely would break even on the cost analysis of an in-furrow fungicide,” Newman said. “Your yield increase would just be enough to pay for the fungicide.”

In 1997, however, “there would again have been a return for using a fungicide, about 200 pounds per acre over the check.”

The take-home message is that a grower can never guess which year is going to be a year in which an in-furrow fungicide is needed, but over time, there is a cost advantage to using one.

Another thing to remember is that every now and then a year comes along when environmental conditions are so severe that nothing, not even fungicides can help. “But that's just the risk you take when you're farming.”

Newman has devised a point system for west Tennessee growers to help them determine if they need an in-furrow fungicide. Some practices that call for an in-furrow fungicide include planting early or when soils or cold and wet, planting in a no-till situation and use of a pre-emergence herbicide or in-furrow insecticide.

In choosing an in-furrow fungicide, Newman suggests you first check with your state Extension Service to make sure that the product is on its recommended list. Secondly, don't cut the rates from what is suggested. Third, make sure that when you're planting early, that the fungicide has the two components for Rhizoctonia and Pythium.

Melvin A. Newman
Soil temperature: 3-day average at 4 inches ____
A. Less than 65 F 100
B. 65 - 72 F 50
C. Higher than 72 F 0
Five-day forecast ____
A. Colder and wetter 100
B. Colder 50
C. Wetter 50
D. Warmer 0
Seed quality: cold germination value ____
A. Less than 59% 100
B. 60 - 69% 50
C. Higher than 70% 0
Field history: based on seedling disease in previous years ____
A. Severe 100
B. Moderate 50
C. Low 0
Tillage: based on field preparation ____
A. No-till 100
B. Minimal tillage 50
C. Conventional 0
Row preparation ____
A. Firm beds present 0
B. Beds not firm 50
C. Bed absent 100
Seeding rate: number of seeds per row foot ____
A. Low: 3 & lower 100
B. Moderate: 5 - 6 50
C. High: 7 & higher 0
In-furrow insecticide/nematicide: Temik, Di-Syston, Thimet, etc. ____
A. Yes 100
B. No 0
Total: if point total exceeds 150, in-furrow fungicide application is suggested ____
This point system is a modified version from a three-year regional cotton project. It should be used as a guide to determine the need for an in-furrow fungicide. It is not a guarantee of economical return.
Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.