Most of the time when downy mildew, caused by Peronospora viciae, appears in edible pod peas, the symptoms are expressed as leaf infections after which some terminal growth becomes systemically infected. Infected leaves become yellow and usually show a purplish-gray growth of sporulating fungus on the undersurface of affected leaves. Systemically infected tissues become stunted, deformed, and also show fungal growth on stems and leaves. Pod production stops on infected terminals. In snow peas little or no pod infection has been observed.
Recently, pea pods from a sugar snap pea planting were submitted for examination. The pods were partially covered with yellow to brownish areas. These areas also showed superficial blistering. Foliage symptoms were for the most part absent or very difficult to find. Initially, the symptoms were thought to be caused by freezing injury as symptoms had appeared soon after a period of several frosty nights. Subsequent examination of plants in the field and microscopic examination of pod tissues show the symptoms to be caused by Peronospora viciae, the pea downy mildew pathogen. In the fields in question, snow peas (Mammoth Melting) and sugar snap peas (Sugar Snap) were growing side by side. The snow peas showed no pod infection, while the sugar snaps showed virtually no foliage infections.
Control of downy mildew in peas is difficult. Copper hydroxide can be used. However, to be at all effective, it has to be applied preventively before disease symptoms appear. Fall- and winter-planted peas on the Central Coast are most prone to infection by Peronospora viciae. A seed treatment of metalaxyl (ApronŽ) will provide early growth protection. Researchers have also reported that foliar nutrients containing phosphorous acid help reduce disease incidence.
The use of foliar nutrients is on the increase. Fertilizers applied to foliage have the benefit of being four to 30 times more efficient. They also provide fairly quick results with little or no risk of leaching to ground water. They are also more costly than conventional fertilizers. However, some knowledge of how rapidly nutrients are assimilated by the host is important in getting the maximum benefit from a foliar application.
The following information is taken from a study done on citrus. Citrus leaves have a substantial layer of cuticle wax and would be more resistant to directly absorbing nutrients than most vegetables with the exception of cole crops. In thin-leafed, tender vegetables the absorption time may be less. Potential phytotoxicity of some of these materials should also be checked before whole field applications are made.
Table 1.
| Urea | 1/2 to 2 hours |
| Magnesium | 2 to 5 hours |
| Potassium | 10 to 24 hours |
| Calcium | 1 to 2 days |
| Manganese | 1 to 2 days |
| Zinc | 1 to 2 days |
| Phosphorus | 5 to 10 days |
| Iron | 10 to 20 days |
| Molybdenum | 10 to 20 days |
Table adapted from Citrograph Magazine, May 1999.
The meeting code is A-0746-99, title: Update - Central Coast Veg IPM, date: 3/31/99, location: Guadalupe, credit: other - 2 hrs. The following persons received 2 hrs. credit for the above meeting:
| Beck, Gerald P. | Moir, Lawrence M. |
| Brackeen, George T. | Nagel, Thomas A. |
| Chaney, William E. | Olivera, James J. |
| Cisney, Ronald W. | Orosco, Frank E. |
| Cisney, Ronald T. | Ouwerkerk, Brenda W. |
| Compton, Peter J. | Parra, Hernan |
| Deguchi, Stanley E. | Perry, John F. |
| Draper, Michael | Pierce, Scott |
| Escalante, Thomas A. | Riddle, Ronald L. |
| Gabel, John E. | Silva, David |
| Kodl, Andrew J. | Smith, Homer L. |
| Krichevsky, Thor A. | Teixeira, Allan C. |
| Laemmlen, Franklin | Tonascia, Gerald |
| Martins, Joseph P. | Vanwie, David M. |
| Mazzucotelli, John J. | Wickham, Joseph A. |
| Mead, Daniel A. | Wunderlich, Lynn R. |
If you have questions about this information, please call Franklin Laemmlen at 805/934-6240.
If you use bees for pollination of crops and you temporarily import hives, make sure you know the origin of the hives and have them inspected. The above precaution also applies to any product that has had prolonged contact with the soil or contains undisturbed soil. Five hundred hives from Texas were recently quarantined and sent back to Texas. Reason - some hives in the shipment were found to be infested with fire ants. This ant could become a serious pest to agriculture and all other forms of life wherever it becomes established in California. It is already present in Orange, San Diego, and Riverside Counties. Erradication efforts are underway. If you find/note unusual ant activity, contact your Agricultural Commissioner or Cooperative Extension office. If you would like some literature about this potential new pest, call 805/934-6240, and we will send you a brochure.