Calcium in White Mold Management of Dry Bean 2000 April 01, 2001
P.L. Gross and R.S. Lamppa, Department of Plant Pathology, NDSU, Fargo, ND
Dry beans are an important crop in North Dakota and Minnesota, which make up the Northarvest Bean Growers Association. Dry bean production reached a peak in 1998 when 940,000 acres were planted. Bean acreage decreased in 1999 and again in 2000 because of lower bean prices. White mold is the worst disease problem effecting dry bean production in the Northarvest region. White mold can be controlled with benzimidazole fungicides, like Benlate (benomyl) and Topsin M (thiophanate methyl). However chemical control is expensive, and only 20% of the bean acres were treated in 1998 in North Dakota (Lamey and others, 1999). Two separate calcium white mold studies were conducted in 2000 using calcium alone and in combination with reduced rates of fungicides. The objective of these studies was to control white mold disease; lower application cost and increase yields. The first study was conducted on six grower fields in three North Dakota counties (Traill, Griggs and Steele). The second study trial was done at the North Dakota State University Irrigated Stations at Oakes and Carrington. Experimental plots at grower fields had six treated strips, 24 to 48 rows wide and ½ to ¾ miles long, with untreated strips adjacent to them. The six treatments were as follows: calcium chloride (1 gal/A) applied at bud stage and 5 days later; calcium chloride (bud stage) + (calcium chloride + benomyl 0.75 lb/A 5 days later); calcium chloride (bud stage) + benomyl at 0.75 lb/A (5 days later); calcium chloride + benomyl applied 5 days after bud, one application of benomyl at 0.75 lb/A and 1.5 lb/A five days after bud stage. The second study was evaluated on the irrigated sites at Oakes and Carrington, ND on four replicated plots with 4 rows that were 25 ft long. The site at Carrington had low levels of white mold and the data will not be presented. Treatments were similar to the grower strip trials except for the calcium + fungicide treatment which had two spray applications. Calcium sulfate was used along with calcium chloride in this study. Since their results were similar the data was combined for analysis.
In the grower plots, white mold developed late in the season because of little precipitation and low humidity during flowering. White mold incidence was significantly reduced by all treatments compared to the untreated check. Two applications of calcium reduced white mold incidence and severity by 16% whereas the fungicide applied at 0.75 lb/A reduced incidence by 20% and severity by 11% compared to the untreated check. Yields were increased by 15% from calcium + fungicide treatment compared to the untreated check.
In the study at Oakes, plants treated with calcium + benomyl with two applications reduced white mold incidence and severity by 41% and 15% compared to the untreated check. Calcium applied alone did not reduce white mold incidence or severity significantly compared to the untreated check. A single application of benomyl applied at 0.75 lb/A reduced white mold incidence by 21% and severity by 10% compared to the untreated check. Yields were increased from 218 to 488 lbs/A when using calcium alone or in combination with a fungicide compared to the untreated check. Calcium applied alone increased yield by 218 lb/A compared the untreated check whereas benomyl alone applied at 0.75 lb/A increased yield by 170 lb/A. White mold incidence was generally low in 2000, with some isolated hot spots. In the replicated calcium study, calcium applied alone at bud stage plus benomyl 0.75 lb/A applied alone 5 days later gave the largest economic return.