Plant Diagnostics

Downy mildew (herbaceous) - Several

Damage

Early symptoms appear as irregular, light green or yellow angular patches on upper leaf surfaces. Lesions may also be purplish red to dark brown. Under high humidity, downy mildews form fluffy or fuzzy (downy) areas of spores on the undersides of leaves. Under magnification, the downy areas look like very small bunches of branched hairs. Older leaves toward the bottom of plants are usually infected first and wither and brown as the disease proceeds up the stem.

Cultural Controls

Downy mildews are favored by low temperatures, and high relative humidity (90%+). Free moisture is required for germination and infection. Spores disperse via the wind. To control downy mildew, provide good air circulation and maintain low humidity. Avoid using overhead irrigation and water plant bases. Rogue affected plants. Purchase downy mildew-resistant varieties of plant stock. At the end of the growing season, remove and destroy infected plant debris which can serve as a source of spores for the next growing season.

Chemical Controls

Azoxystrobin
Signal Word: Caution
Pesticide Class: Systemic-Upward only
Boscalid+Pyraclostrobin
Signal Word: Caution
Pesticide Class: Local Protectant
Chlorothalonil
Signal Word: Warning
Pesticide Class: Protectant
Copper
Signal Word: Caution
Pesticide Class: Protectant
Copper hydroxide
Signal Word: Danger
Pesticide Class: Protectant
Copper sulfate
Signal Word: Caution
Pesticide Class: Protectant
Copper+Mancozeb
Signal Word: Danger
Pesticide Class: Protectant
Cyazofamid
Signal Word: Caution
Pesticide Class: Protectant
Fenamidone
Signal Word: Warning
Pesticide Class: Protectant
Fludioxonil+Mefenoxam
Signal Word: Caution
Pesticide Class: Protectant, Systemic-upward only
Fosetyl-aluminum
Signal Word: Caution
Pesticide Class: Systemic
Imazalil
Signal Word: Caution
Pesticide Class: Systemic-upward only
Kresoxim-methyl
Signal Word: Caution
Pesticide Class: Local protectant
Mancozeb
Signal Word: Caution
Pesticide Class: Protectant
Mancozeb+Thiophanate-methyl
Signal Word: Caution
Pesticide Class: Protectant, systemic-upward only
Mefenoxam
Signal Word: Warning
Pesticide Class: Systemic-upward only
Phosphorous acid
Signal Word: Caution
Pesticide Class: Systemic
Polyoxin-D Zinc Salt
Signal Word: Caution
Pesticide Class: Local protectant
Pyraclostrobin
Signal Word: Caution
Pesticide Class: Local protectant
Trifloxystrobin
Signal Word: Caution
Pesticide Class: Local protectant

Locations Affected

flowers, fruit, leaves, stem

Plant Environment

greenhouse, outdoors

Scouting Season:

January - Early , January - Mid , January - Late , February - Early , February - Mid , February - Late , March - Early , March - Mid , March - Late , April - Early , April - Mid , April - Late , May - Early , May - Mid , May - Late , June - Early , June - Mid , June - Late , July - Early , July - Mid , July - Late , August - Early , August - Mid , August - Late , September - Early , September - Mid , September - Late , October - Early , October - Mid , October - Late , November - Early , November - Mid , November - Late , December - Early , December - Mid , December - Late

Plants Affected


© 2013 Board of Regents of the University of Wisconsin System, doing business as the Division of Cooperative Extension of the University of Wisconsin-Extension. If you have any questions regarding this site's contents, trouble accessing any information on this site, require this information in an alternative format or would like to request a reasonable accommodation because of a disability email: greenindustry@ces.uwex.edu