Fusarium wilt of safflower is caused by the soil-borne fungus Fusarium oxysporum f. sp. carthami. The Fusarium wilt fungus occurs in most cultivated soils of the region where safflower have been grown previously, and many plants grown in these soils may become infected to some degree before they mature. Disease severity is favored by high temperature stress, poor drainage, and soil compaction, especially when safflower is grown in acidic, light-textured soils high in nitrogen. In general, any factor which contributes to a reduced rate of root growth increases the plant's susceptibility to Fusarium wilt. Early planting in cool, moist soil favors the disease. High plant populations also increase plant stress and favor infection. Improper cultivation, other soil-borne pathogens, and various herbicides are also known to induce injury of young roots and aggravate Fusarium wilt damage. The effect of Fusarium wilt is most apparent during flowering when the plant and its productivity are more sensitive to stress. The pathogen is disseminated within and among fields by the movement of contaminated soil and conidia by wind, irrigation water, and on equipment. The pathogen can survive between safflower crops as dormant chlamydospores or in infested crop debris.
Above-ground symptoms of Fusarium wilt appear on lower leaves which exhibit yellowing and wilting, which become more pronounced and progress upward into younger leaves. Often chlorosis is only on one side of the a diseased plant. Stunting is evident, especially if plant infection and stress occurred during the seedling and vegetative stages. The margin of infected leaves turns tan to brown and diseased plants become progressively more yellow. Severely infected plants exhibit permanent wilting and premature defoliation. Vascular discoloration on the main stem is the diagnostic symptom and is usually evident after the initial appearance of foliar symptoms. The reddish brown vascular discoloration of root, stem, and petiole tissue of infected plants will vary considerably in intensity, depending on varietal reaction, severity of infection and environmental conditions. The heads of diseased plants are distorted and blighted, and often have aborted seed. Yield losses may approach 100% if susceptible varieties are grown in fields with a history of severe Fusarium wilt.
Incorporation of organic matter may reduce Fusarium wilt by improving soil tilth and water holding capacity.
Plant high quality seed free of the Fusarium wilt pathogen in warm, well-prepared seedbeds under conditions favorable to rapid seedling emergence. Resistant varieties are available to race 4 of F. oxysporum f. sp. carthami and should be planted. Avoid planting in fields with a history of root rot and wilt problems. A three-year or longer rotation to non-hosts such as small grains or corn reduces wilt severity. Chiseling (sub-soiling) 10 to 20 inches deep between safflower rows promotes root penetration and improves plant tolerance to wilt, but avoid root injury during field operations. Manage irrigation to eliminate moisture stress to the developing plant, but avoid excess water that may deprive roots of oxygen. Avoid dense plantings. Space plants at least two to three inches apart within the row to reduce plant competition for water.
Seed treatments can reduce surface contamination by the Fusarium wilt pathogen, but are most effective when combined with sound cultural practices.
Product List for Fusarium Wilt:
Pesticide |
Rate per 100 lb seed |
Application Frequency (days) |
Remarks |
|
Captan |
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|
Captan 75 |
6-9 oz |
Seed treatment |
Broad spectrum, but weak against Pythium and Phytophthora spp. |
|
Captan 30-DD |
1.25 fl oz |
Seed treatment |
Broad spectrum, but weak against Pythium and Phytophthora spp. |
|
Captan 400 |
1-2 fl oz |
Seed treatment |
Broad spectrum, but weak against Pythium and Phytophthora spp. |
|
Captan 400-C |
1-2 fl oz |
Seed treatment |
Broad spectrum, but weak against Pythium and Phytophthora spp. |
|
Carboxin and Carboxin + Thiram |
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|
Vitavax 34 |
2 fl oz |
Seed treatment |
Suppression of Rhizoctonia |
|
Vitavax 200 |
4 fl oz |
Seed treatment |
Broad spectrum |
|
EBDC—several formulations available, but not all are listed |
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|
Dithane M45 |
2 oz |
Seed treatment |
Broad spectrum |
|
Fludioxonil |
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|
Maxim 4FS |
0.08-0.16 fl oz |
Seed treatment |
Suppression of Fusarium and Rhizoctonia spp. |
|
Thiram |
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|
42-S Thiram |
8 fl oz |
Seed treatment |
Broad spectrum |
|
Thiram 50WP |
8 oz |
Seed treatment |
Broad spectrum |
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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: Safflower, Disease, Fusarium Wilt
Date: 3/3/2005