Alternaria leaf spot is caused by the fungus Alternaria brassicicola, and is generally only a problem on cabbage and Chinese cabbage during extended cool, rainy weather. Broccoli and cauliflower are rarely infected by this pathogen. Infection occurs when windblown spores land on leaves and infect through natural openings, wounds, or directly penetrate the leaf. Lesions on diseased plants release abundant spores during dry periods, and alternating cycles of evening leaf wetness followed by daytime drying favor disease and sporulation. The pathogen survives between susceptible hosts in crop debris and on seed.
Alternaria leaf spot lesions first appear as small, dark areas that develop into large, circular lesions with concentric rings that resemble a bull’s-eye pattern. A lesion appears dark brown when wet, but when dry the lesion appears velvety. The disease reduces the photosynthetic area of infected plants, but may also cause lesions on brussel sprouts.
No biological control strategies have been developed for Alternaria leaf spot.
Plant only high quality seed free from the Alternaria leaf spot pathogen. Practice a three-year or longer rotation to non-hosts. Deeply incorporate crop residues after harvest to reduce pathogen survival. Avoid overhead irrigation where possible. Promote air movement in the canopy by planting wide rows parallel to the prevailing wind direction. If possible, irrigate so that the canopy dries before dusk to prevent extended periods of leaf wetness.
Fungicides are most effective when used in combination with cultural control strategies.
Product List for Alternaria Leaf Spot:
Pesticide |
Product per Acre |
Application
Frequency
|
Remarks |
Azoxystrobin |
|||
|
Quadris |
6.2-15.4 fl oz |
7-14 days |
Maximum of 3 applications or 2.88 quarts per season; Do not make more than 1 application of Quadris before rotating to a fungicide with a different mode of action; 0 day PHI |
Chlorothalonil and Chlorthalonil Mixtures |
|||
|
Bravo Ultrex |
1.4 |
7-10 days |
Maximum of 14.5 pounds per season; 7 day PHI |
|
Bravo Weather Stik |
1.5 pt |
7-10 days |
Maximum of 16 pints per season; 7 day PHI |
|
Echo 720 |
1.5 pt |
7-10 days |
Maximum of 2 gallons per season; 7 day PHI |
|
Echo 90DF |
1.25 lb |
7-10 days |
Maximum of 13.3 pounds per season; 7day PHI |
|
Echo Zn |
2.25 pts |
7-10 days |
Maximum of 2.9 gallons per season; 7 day PHI |
|
Ridomil Gold/Bravo |
1.5 lb |
14 days |
Make 2 to 4 total sprays; 7 day PHI |
Copper Fungicides and Copper Mixtures |
|||
|
Basicop |
3-4 lb |
7-14 days |
Crop injury can occur |
|
Champ Dry Prill |
0.33-0.66 lb |
7 days |
Crop injury can occur |
|
Champ Formula 2 |
1.33 pt |
5-7 days |
Crop injury can occur |
|
Copper-Count-N |
1-3 qt |
7-10 days |
Crop injury can occur |
|
Cuprofix Disperss |
1.5-2.5 lb |
5-10 days |
Crop injury can occur |
|
Kocide 3000 |
0.5-0.75 lb |
7-10 days |
Reddening of older leaves may occur on broccoli and a flecking of wrapper leaves may occur on cabbage |
|
Ridomil Gold/Copper |
1 pack/per 2.5 acres |
14 days |
Make 2 to 4 total sprays; 7 day PHI |
|
Top Cop + S |
4 pt |
7-10 days |
Crop injury can occur |
|
Cyprodinil / Fludioxonil |
|||
|
Switch 62.5WG |
11-14 oz |
7-10 days |
After 2 applications, rotate with other mode of action; Maximum of 56 oz/A; 7 day PHI |
|
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. |
|||
Categories: Cole Crops, Disease, Alternaria Leaf Spot
Date: 04/01/2007