What fungicide do I choose for disease control in strawberries?
May 9, 2006 - Author: Annemiek Schilder, Michigan State University Extension, Department of Plant Pathology
Editor’s note (2011): This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Editor’s note (2006): This article was originally published on May 5, 2004, in the Fruit CAT Alert. It is being republished at this time for your convenience.
There are more choices for disease control in strawberries than ever before. This can be a rather bewildering experience, as growers have to consider the disease control spectrum, efficacy ratings and cost per acre for each product. This article aims to help strawberry growers in the decision-making process by outlining unique aspects of several strawberry diseases, characteristics of the newer fungicides, and by suggesting several possible fungicide programs. A few notes on specific diseases:
1) Control of leaf diseases, such as common leaf spot, scorch, Phomopsis leaf blight and angular leaf spot may only be needed on susceptible cultivars. Some leaf diseases can spread to the berries (e.g., Phomopsis can also cause a fruit rot), or berry caps (angular leaf spot and scorch). If these have been a problem in the past, start fungicide sprays before bloom.
2) Leather rot (Phytopthora cactorum) is best controlled by growing strawberries in well-drained soil and by applying straw mulch between the rows to prevent the berries from touching the soil (where the fungus resides) and prevent soil from splashing up onto the berries. If there still is a problem, use Ridomil Gold or Aliette for control. Some phosphorous acid products such as Agri-Phos (similar to Aliette) may also work, but have not been evaluated on strawberries in Michigan. Spray during bloom and fruit development.
3) Angular leaf spot is a bacterial disease characterized by translucent leaf spots and blackening of the berry caps. It is favored by cool, wet weather and nights with temperatures close to freezing. The bacteria are spread by rain splash or by irrigation water. Copper (e.g., Kocide, Cuprofix, Bordeaux, etc.) is the only chemical that works against this disease. Some labels suggest adding lime as a safener to reduce the risk of crop injury. In susceptible varieties, start spray applications before bloom to prevent multiplication of the bacteria on the leaves before they jump to the berry caps.
4) Botrytis gray mold, the predominant fruit rot in most areas where strawberries are grown, primarily enters the berries through the blossoms, which means that chemical control should be focused on the bloom period. The Botrytis fungus can produce numerous spores on dead leaves and other plant matter and spreads easily by wind. Make sure to protect the king blooms especially, since these provide the largest berries. The other period for control is pre-harvest, since Botrytis can spread rapidly from infected berries to ripe and overripe berries. Pre-harvest sprays reduce post-harvest rots and increase shelf life of the berries.
5) Most other fruit rots, including anthracnose, tend infect the berries somewhat later in the season, i.e., during the green fruit or ripening stage. Anthracnose fruit rot is favored by warm, humid conditions and can spread rapidly during rains or frequent irrigation. In cool seasons, it tends to appear closer harvest or may not show up at all. Anthracnose fruit rot can be identified by black sunken lesions with wet, orange (and sometimes gray) spore masses in them. The anthracnose fungus is able to multiply on the leaves without visible symptoms, which may explain its sometimes widespread and sudden appearance in fields.
New fungicide characteristics (prices are estimates for comparative purposes only and may vary depending on the supplier and quantity purchased). Please follow label directions carefully before use.
Pristine (pyraclostrobin and boscalid) contains a strobilurin and an analid active ingredient. This fungicide is a very broad-spectrum material and has excellent activity against leaf spots, powdery mildew, and fruit rots, including Botrytis gray mold. It is surface-systemic (i.e., it is somewhat mobile within the wax layer on the plant surface) and has limited back action. The fungicide gets rainfast quickly. The label rate is 18-23.5 oz/acre (approximate cost: $32-$42/acre). The number of applications is restricted for fungicide resistance management. PHI=0 days.
Cabrio (pyraclostrobin) is a strobilurin-type fungicide with excellent broad-spectrum activity against leaf spots, powdery mildew and fruit rots . However, it does not provide much control of Botrytis gray mold. It is surface-systemic and has limited back action. The fungicide gets rainfast quickly. The label rate is 12-14 oz/acre (approximate cost: $16-$18/acre). The number of applications is restricted for fungicide resistance management. PHI=0 days.
Abound (azoxystrobin) is also a strobilurin-type fungicide with good to excellent broad-spectrum activity against leaf spots, powdery mildew and fruit rots. It does not have much activity against Botrytis gray mold. It is surface-systemic and has limited back action. The fungicide gets rainfast quickly. The label rate is 6.2-15.4 fl oz/acre (approximate cost: $12-$30/acre; $24 at the 12-oz rate). The number of applications is restricted for fungicide resistance management. PHI=0 days.
Elevate (fenhexamid) is a fungicide with a new chemistry that has excellent activity against Botrytis gray mold. While fenhexamid has some systemic activity, it should be used as a preventative fungicide. The fungicide gets rainfast quickly. Can be used to alternate with fungicides in other chemical classes. The label rate is 1.5 lb/acre (approximate cost: $41/acre). PHI=0 days.
Captevate (fenhexamid and captan) is a pre-mix of Elevate and Captan. It has excellent activity against Botrytis as well as moderate to good activity against anthracnose and other leaf spot and fruit rot diseases. This formulation appears to perform a bit better than a tank mix of Elevate and Captan. The label rate is 3.5-5.25 lb/acre (approximate cost: $42-$63/acre) . At the high rate, the dose is equivalent to 1.5 lb Elevate and 5 lb Captan. The PHI=0 days.
Switch (cyprodinil and fludioxonil) is a mixture of a systemic and protectant active ingredient (both are new chemistries). Switch has excellent activity against Botrytis gray mold and moderate to good activity against anthracnose and scorch. The label rate is 11-14 oz/acre (approximate cost: $39-$50/acre). PHI=0 days.
Older fungicides such as Topsin M, Captan, Thiram, Sulfur, etc. remain effective disease control tools. The approximate prices per acre: Topsin M $16/acre; Captan $13/acre; Thiram $8/acre; Sulfur $1-2/acre; and copper formulations: $3 to $4/acre.