Traill County Ag Alert Newsletter

Traill County Ag Alert Newsletter

August 7, 2008

Issue #14 August 7, 2008

RAINFALL & GROWING DEGREE DAYS (GDD)

Location                                 Mayville                      Hillsboro                    Galesburg
Corn GDD                              1324                            1341                                1340
Compared to 2007                   -272                             -260                              -245
5 Year Average                        -134                             -120                                -74

Rainfall since June 1 8.79 inches 9.19 inches 8.07 inches

*Wheat is turning and we will be harvesting soon and therefore I have chosen not to include the Wheat GDD numbers.

WHITE MOLD IN BEANS
Recent weather conditions are conducive to the growth of white mold in Dry Beans and Soybeans. On Thursday, July 31 white mold was found in an area navy bean field, near Buxton reported by Eben Spencer (ADM).

White mold is difficult to eliminate because the fungus forms tough black to grayish bodies called sclerotia which can survive more than 10 years in the soil. Sclerotia produce fungus fruiting bodies at cool temperatures of about 60 degrees F when there is rain or heavy dew. The fruiting bodies invade the plants and the white mold disease develops in moderate temperatures of about 75 degrees F.

The infection and spread of white mold may appear to be rapid and a whole field can be lost in a few days after initial symptoms are detected.

Infected plants first develop small, water-soaked spots on the pods, stems or foliage. The spots enlarge to form large masses of soft-rotted tissue covered with masses of white moldy fungus growth.

Scout each field and evaluate each field when determining the need to apply a fungicide. There are a number of registered herbicides that are labeled for the control of White Mold including Boscalid (Endura), Cyprodinil + Fludioxonil (Switch 62.5 WG), Iprodione (Rovarl 4F), Prothioconazole (Proline 480 SC) and several formulations of Thiophanate-methyl. As always refer to the label for rates, application timing and pre-harvest interval.

SECOND GENERATION BEAN LEAF BEETLE IN SOYBEANS
A few soybean fields in southeastern North Dakota have reported with low levels of bean leaf beetles (BLB) in soybeans. This is the 2nd generation of BLB, and the most important in terms of potential yield impact due to its pod feeding. This causes pod scarring, pod clipping and decreased seed quality. Fungal pathogens can also infect injured pods causing discolored, shrunken or moldy pods. Adult BLB are 5 mm long with yellow or red wing covers with four black spots and black margin around the edges of the wing covers. The main identification characteristic is the black triangle behind the head. Feeding injury symptoms include round holes between leaf veins.

It is a difficult insect to scout for, because it often hides or drops to soil when it sees you approaching. Sweep nets can also be used for monitoring or detecting beetles. Treatment would be recommended when 3 to 7 beetles per sweep are found. Economic threshold is 25% defoliation from reproductive pod fill to maturity or 10% pod feeding (or the presence of clipped pods).

BACTERIAL BLIGHT SHOWING UP ON DRY BEANS
In the last week, bacterial blights have shown up in dry beans. Three different bacterial blights are found on dry beans; common bacterial blight, halo blight, and bacterial brown spot. Each disease is spread by rain splash, and the diseases are frequently worse when the plants are injured by wind or hail. Several strong storms have moved through in the last two weeks, and this has contributed to the development of the diseases.

Although multiple diseases can occur at the same time and on the same plants, each disease has different symptoms.

Leaf symptoms:

Halo blight appears as small water soaked lesions and often produces a large yellow-green halo. When temperatures are hot, the halo’s may be smaller. Early symptoms of bacterial brown spot also appear as a small water soaked lesion but have a small yellow-green halo, often with a very defined border. As bacterial brown spot develops, the lesions turn brown and the centers fall out. Heavily infected plants look like they were shot by a shotgun.

Common bacterial blight lesions begin on the edge of the leaf as a scalded area with water-soaked spots. Common bacterial blight lesions enlarge quickly and are bigger (up to an inch) than the other two bacterial diseases, and often have a narrow yellow border.

Pod Symptoms: Symptoms of halo blight and common blight are similar. Both diseases begin as water-soaked spots or streaks on the pod surface. As the lesions develop, they may be surrounded by a reddish-brown zone. Under humid conditions, a cream-colored exudate may be present in halo blight lesions, whereas a yellow exudate may be present in common bacterial blight lesions.

Bacterial brown spot lesions begin as small water-soaked lesions, but become sunken brown spots. Pods with bacterial brown spot infections may be bent or twisted at the site of infection.

The biology and management of each disease is similar. Bacterial blights can survive in seed, bean residue, and sometimes weed hosts. Once the diseases are present, they can spread quickly if heavy rains and adverse weather conditions (high winds, hail, etc.) occur. Unfortunately, little can be done this season to manage bacterial diseases. Although copper fungicides are sometimes used in other regions of the country (dryer western states like Colorado), little success has been observed in North Dakota. Management for future years is important if you have bacterial blights in your fields.

Clean seed, rotation, and good sanitation are all recommended. Although these practices are not a guarantee you will not have bacterial blights, they minimize the likelihood of getting the diseases. If you have bacterial blights in your field now, it is critical not to keep that seed for planting in the future.

CERCOSPORA LEAFSPOT IN SUGAR BEET
It is the season for Cercospora leafspot, the most damaging foliar disease of sugarbeet which reduces tonnage and sucrose content. Cercospora leafspot develops rapidly in warm, humid, and rainy weather. The Cercospora spores are produced at temperatures of 68 to 79 F and relative humidities (RH) of 90-100 %. Spore release is effected by rain and dew. Optimal spore germination and infection occurs when the temperature is 75-77° F and the RH is 100 % for at least 8 hours. Day temperatures of 80- 90 F and night temperatures above 60 F favor disease development. Leafspot symptoms may occur about 5-21 days after infection depending on prevailing weather conditions. Cercospora infection produces circular spots about 1/8 of an inch in diameter with ash gray centers and dark brown or reddish-purple borders. As the disease progresses, individual spots coalesce and kill entire leaves, particularly on susceptible varieties. In humid conditions, the spots become gray and velvety with the production of spores. These spores further spread the disease, especially within fields, resulting in many infection cycles during the growing season.

As such, it is important to have early control of Cercospora leafspot. The best manner to control leafspot is by using an integrated approach that include cultural practices such as burying infected tops by tillage, planting tolerant varieties in fields with a minimum rotation interval of three years, and the timely and proper use of recommended fungicides.

At this time growers should scout fields for disease symptoms. First symptoms will be observed in fields with less tolerant varieties that are close to windbreaks, in sheltered areas, and those close to rivers. The first fungicide application should be made when symptoms are first observed. It is very important that the first fungicide application be applied in a timely manner or effective disease control will be difficult to achieve for the remainder of the season. Subsequent fungicide applications should be based on the presence of disease and favorable conditions for disease development. Please check the NDAWN website http://ndawn.ndsu.nodak.edu/ for information on the favorability of environmental conditions for development of Cercospora leaf spot.

NDSU Extension Service, North Dakota State University of Agriculture and Applied Science, and U.S. Department of Agriculture cooperating, Duane Hauck, Director,
Fargo, North Dakota. Distributed in furtherance of Acts of Congress of May 8 and June 30, 1914. We offer our programs and facilities to all persons regardless of race,
color, national origin, religion, sex, handicap, age, Vietnam era veteran status, or sexual orientation; and are an equal opportunity employer.

Go to Traill County Agriculture Program Page

Go to Traill County Home Page

Traill County Extension Office

P.O. Box 730

Hillsboro, ND 58045

701-636-5665 or toll-free1-877-843-6383