Seminole Crop E News

Agricultural News for Farmers and Agribusiness in SW Georgia

Late Leafspot a Problem in Peanuts

Posted by romeethredge on October 9, 2014

We are seeing more and more late leafspot in peanuts. Here’s a field of irrigated Ga o6G peanuts that are 125 days old. They have been sprayed with fungicides all season but we have a problem. We’ve lost most of our leaves to the disease.

 

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Management Points for Leaf Spot, UGA Peanut Production Update 2014

1. Practice good crop rotation.

2. Destroy any volunteer peanuts that may grow in a field and bury/remove old peanut
hay that can serve as a source of spores for leaf spot diseases.

3. Do not delay the start of a leaf spot fungicide program.

a. When using chlorothalonil (e.g. Bravo Ultrex, Bravo WeatherStik, Echo,
Equus, or other generics), Tilt/Bravo, Echo-PropiMax, Stratego, Elast 400F,
Eminent 125SC + Echo, or Headline (at 6 fl oz/A), and you have adequate
crop rotation, your first leaf spot spray will typically be applied somewhere
between 30 and 35 days after planting (unless weather has been dry and
unfavorable for development of foliar diseases.

b. In fields where risk to leaf spot has been calculated as low-to-moderate, we
have maintained good control of leaf spot when using a single application of
Tilt/Bravo (2.5 pt/A) 40 days after planting

c. Growers who use the AU-pnut forecasting system, automated at
http://www.AWIS.com, can more effectively time their first application based upon
environmental conditions.

d. If you are planting peanuts after peanuts, you will likely need to begin your
leaf spot program earlier than 30 days after planting because of the increased
risk of disease.

e. If you are using Headline (at 9 fl oz/A) for your first leaf spot spray, it is
appropriate to combine your first two fungicide applications for leaf spot
control (for example at 30 and 44 days after planting) into a single application
of 9 oz of Headline at 38-40 days after planting.

4. Traditionally, fungicides are applied on a 14-day calendar schedule beginning after
the first application. This 14-day interval may be modified for reasons such as those
below:

a. The interval should be shorter than every 14-days if conditions:

i. Rainfall has been abundant and conditions are favorable for leaf spot.

ii. You are using the AU-PNUT leaf spot advisory and it calls for an early
application.

iii. Peanuts follow peanuts in a field and leaf spot is expected to be
severe.

iv. Rainfall came on quickly after your last leaf spot spray and you are
concerned that some of the fungicide may have been washed off the
plants in the field too quickly.

v. You are planting a variety that has poor resistance to leaf spot
diseases.

vi. Peanut rust appears in your field prior to the end of the season.

b. It may be possible to extend the spray interval beyond 14-days if:

i. Conditions have been dry and unfavorable for leaf spot, especially if
you use the AU-PNUT advisory for spray guidance.

ii. You are using a variety with increased resistance to leaf spot. For
example, if pressure from soilborne diseases is not severe, the spray
interval for such varieties could be every 21 days and it is possible to
treat the most resistant varieties only three times during the season.
(Additional information can be obtained from your local Extension
Agent).

iii. You use Peanut Rx and determine that the predicted risk of
fungal disease in a field is low to moderate and rainfall has not
been excessive since your last spray (additional information can be
obtained from your local Extension Agent).

iv. Since many fungicide applications are used to manage leaf spot
diseases and soilborne diseases, one must consider the effect that an
extended spray schedule would have on both types of disease (foliar
and soilborne) BEFORE shifting from a 14-day schedule.

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