Nematode angular leaf spot (NALS), caused by Aphelenchoides ritzemabosi, is a recent disease of dry bean first described in 1993. Infection is enhanced by moisture, because the nematode can swim in the water film on the plant surface. When favorable conditions exist, the nematode can feed on the epidermis and also invade leaves through stomates, where it subsequently feeds and reproduces. The presence of the nematode in leaves initiates lesion development and eventual breakdown of the mesophyll. Larger leaf veins initially limit lesion expansion, however, with advanced stages of parasitism, widespread necrosis across leaf veins can occur. It is likely that cool, wet environmental conditions increase the risk of NALS development and the probability of observing symptoms in the field.
Infection of dry bean by A. ritzemabosi results in numerous dark, angular lesions on leaves and, occasionally, a superficial necrosis on the upper surface of the petiole. Inoculated unifoliolate and trifoliolate leaves may develop angular lesions after approximately 11 days at 72°F, which may become more obvious 14 to 20 days after inoculation. Increased leaf senescence occurs as incubation time increases. Expansion of individual lesions is limited by leaf veins, with most lesions ranging in size from 0.1 to 0.4 inch. Occasionally, large sections of leaflets, or entire inoculated leaflets, become chlorotic or necrotic within 24 days after inoculation.
Parasitism of dry bean by Aphelenchoides ritzemabosi may cause yield loss because photosynthetic leaf area is destroyed during nematode feeding and reproduction. However, parasitized fields were rarely found in Wyoming during a three-year survey and the number of affected plants in a field was small. Therefore, it is unlikely that NALS will cause economic yield loss unless circumstances for nematode survival and foliar parasitism are unusually favorable.
Incorporation of green manure crops such as sudangrass, sesame, rapeseed, white mustard, or perennial ryegrass the season before dry beans are planted can reduce some nematode populations.
Plant certified seed. Practice a three-year or longer rotation, but avoid dry bean rotations with alfalfa. Promptly incorporate crop debris to encourage breakdown of leaf material.
Chemical nematicides may be effective but are expensive and may not be justified unless yield losses are high. Nematicides used on a previous crop in the rotation, i.e., sugar beet or potato, may exhibit some beneficial carryover effects on the following bean crop.
Product List for Nematode Angular Leaf Spot:
Pesticide |
Product per acre |
Remarks |
Nematicide/Insecticide |
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Mocap EC |
2.0-2.9 fl oz/1000 ft banded 1-1.33 gal broadcast |
Restricted use; preplant incorporate 2 to 4” deep. |
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Temik 15G |
7.5-15 oz/1000 ft banded 7-14 lb broadcast |
Restricted use; drill 2-3” below or to the side of seed; 90 day PHI |
Fumigant |
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Restricted use; Preplant application, aerate 7-14 days. |
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Telone C-17 |
10-17 gal |
Restricted use; Preplant application, aerate 7-14 days. |
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Vapam |
40-100 gal |
Restricted use; Preplant application, aerate 7 days. |
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The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality. |
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Categories: Dry Bean, Disease, Nematode
Date: 04/01/2007