Gummy stem blight is caused by the fungus Didymella bryoniae (anamorph Phoma cucubitacearum). The pathogen can also attack fruit, causing a disease known as black rot. The disease cycle begins when spores (ascospores) are released from fungal fruiting bodes after rain or heavy dews. When these ascospores land on leaves and stems, they infect through natural openings, wounds, or by direct penetration. Young leaves of watermelon and melon are highly susceptible to infection, but cucumber and squash are resistant when young and become susceptible as they age. Fruit can be infected through wounds and flower scars at pollination. Infection is favored by free moisture and cool to moderate (68 to 77ºF) temperatures, but continuous leaf wetness is essential for disease to progress significantly. The pathogen can be disseminated within and among fields by wind and splashing water, and survives between cucurbit crops in infested crop debris and diseased vines.
Gummy stem blight symptoms first appear on leaves as circular, tan to dark brown spots, with or without water-soaking. Lesions often develop first at leaf margins, but eventually entire leaves become covered with lesions. Stem lesions are circular in shape, and tan to dark brown in color. Stem cankers develop on cortical tissues and often produce brown, gummy exudates. Small black specks, fruiting bodies of the fungus, are apparent on stem cankers. Seedlings can be killed from stem girdling. Lesions develop more slowly if infection occurs in older plants, and cankered vines wilt near mid-season. Fruit lesions appear as small, water-soaked spots that enlarge; gummy exudates are apparent on fruit. Gummy stem blight can reduce yield, quality, and marketability of fruit.
No biological control strategies have been developed for gummy stem blight.
Practice a two-year or longer crop rotation to nonhosts. Promote air movement within the plant canopy and rapid leaf drying by avoiding dense plantings, narrow row spacings, and excess and overhead irrigation. Orientating rows parallel to the prevailing wind direction can also help reduce periods of leaf wetness in semi-arid environments. Resistance to gummy stem blight is not available in commercially-acceptable watermelon, cucumber, or melon varieties.
Seed treatments should be routine practice for gummy stem blight control. Regular fungicide sprays may be necessary to control gummy stem blight during cool, rainy weather. Resistance to benzimidazole fungicides (such as Topsin-M) and azoxystrobin (Quadris) has been reported in the eastern U.S. and may appear in the High Plains with repeated use of these fungicides.
Product List for Gummy Stem Blight and Black Rot:
Pesticide |
Product per acre |
Application Frequency
|
Remarks |
Captan |
|||
|
Captan 4F |
4 pt |
5-7 days |
4 day REI |
|
Captan 50 |
4 lb |
5-7 days |
4 day REI |
Chlorothalonil and Chlorothalonil Mixtures |
|||
|
Bravo 720 |
|
|
Do not graze or feed debris to livestock; 7 day PHI |
|
Bravo Ultrex |
1.4-1.8 lb |
7-10 days |
Maximum of 16.5 pounds per season; 0 day PHI |
|
Bravo WeatherStik |
1.5-2.0 pt |
7-10 days |
Maximum of 20 pints per season; 0 day PHI |
|
Echo 720 |
1.5-2.0 pt |
7-10 days |
Maximum of 2.5 gallons per season; 7 day PHI |
|
Echo 90DF |
1.2-1.6 lb |
7-10 days |
Maximum of 16.67 pounds per season; 7 day PHI |
|
Echo Zn |
2.2 to 2.8 pt |
7-10 days |
Maximum of 3.6 gallons per season; 7 day PHI |
|
Ridomil/Bravo |
1-2 lb |
7-14 days |
7 day PHI |
Copper Fungicides |
|||
|
Champ Dry Prill |
1.33 lb |
5-7 days |
|
|
Champ Formula 2 |
1.33 pt |
5-7 days |
|
|
Copper-Count-N |
4-6 pt |
7 days |
Mid-harvest. |
|
Kocide 101 |
1.5-3 lbs |
5-7 days |
May cause injury |
|
Kocide DF |
1.5-3 lbs |
5-7 days |
May cause injury |
|
Kocide 4.5LF |
1-2 pts |
5-7 days |
May cause injury |
|
Kocide 3000 |
0.5-1.25 lb |
5-7 days |
May cause injury |
|
Nordox |
1.5-2.0 lb |
7-10 days |
|
|
Tri Basic Copper |
2-4 pt |
7-10 days |
1 day PHI |
EBDC and Copper/EBDC Mixtures |
|||
|
Cuprofix MZ Disperss |
4-7.25 lb |
3-7 days |
Maximum of 63.1 pounds per season; 5 day PHI |
|
Dithane |
2-3 lb |
7-10 days |
Maximum of 25.6 pounds per season; 5 day PHI; use a non-ionic surfactant to improve performance |
|
Maneb 75 DF |
1.5-2.0 lb |
7-10 days |
Maximum of 17.1 pounds per season; 5 day PHI |
|
Manex 80W |
1.5-2.0 lb |
7-10 days |
Maximum of 16.0 pounds per season; 5 day PHI |
|
Manex |
2.4-3.2 pt |
7-10 days |
Maximum of 25 pints per season; 5 day PHI |
|
ManKocide |
2.0-2.5 lb |
7-10 days |
Maximum of 128 pounds per season; 5 day PHI |
|
Penncozeb 80W |
1.5-3.0 lb |
7-10 days |
Maximum of 24.0 pounds per season; 5 day PHI |
|
Penncozeb 75DF |
1.5-3.0 lb |
7-10 days |
Maximum of 25.6 pounds per season; 5 day PHI |
Strobilurins and Strobilurin Mixtures |
|||
|
Cabrio |
12-16 oz |
7-14 days |
Maximum of 4 applications or 64 oz per season; Alternate with different modes of action; 0 day PHI |
|
Quadris |
11.0-15.4 fl oz |
5-14 days |
Maximum of 4 applications or 2.88 quarts per season; Alternate Quadris with fungicides with different modes of action; 1 day PHI |
Thiophanate Methyl |
|||
|
Topsin M 70WP |
0.5 lb |
7-14 days |
Maximum of 3 lb per season; Alternate fungicide sprays or tank-mix with fungicides with a different mode of action; 1 day PHI |
|
Topsin 4.5 FL |
10 fl oz |
7 days |
Maximum of 60 fl oz per season; Alternate fungicide sprays or tank-mix with fungicides with a different mode of action; 1 day PHI |
|
Topsin WSB |
0.5 lb |
7-14 days |
Maximum of 3 lb per season; Alternate fungicide sprays or tank-mix with fungicides with a different mode of action; 1 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: Cucurbits, Disease, Gummy Stem Blight, Black Rot, Cucumber, Melon, Pumpkin, Squash, Zucchini
Date: 04/01/2007