Posts Tagged ‘phytophthora phaseoli’

Scout Lima Beans for Disease

Friday, August 20th, 2010

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

At this time last year downy mildew on lima beans had been seen. So far weather conditions have not been favorable for downy mildew. It looks like the weather may be changing and getting a bit cooler with more dew and possibly fog in the early morning hours. If it should start raining soon growers and crop consultants should be scouting for downy mildew. Race F of Phythophthora phaseoli was the only race identified in 2006, 2008 and 2009.

Preventative applications of 2 lbs fixed copper, 2 lbs Ridomil Gold/Copper, or 3- 4 pts Phostrol have provided control of downy mildew in the past. The newest formulation of fixed copper from DuPont is Kocide 3000 and it performs as well as the other formulations of copper at the rate of 1.3 lbs/A. The best controls continue to be Ridomil/Gold Copper, Phostrol or other labeled phosphonate fungicides, especially when disease pressure is high. Application at flowering or when pods are first forming is recommended if weather is favorable for disease. If disease is present Ridomil/Gold Copper and Phostrol have shown to provide some curative activity if applied when downy mildew is first seen. If downy is present in the field do not use copper fungicides alone for curative control, they will not provide control. Another product that is labeled on lima beans for white mold control is Omega but not downy mildew, but in DE this would be a 2ee use that someone like myself can recommend since the fungicide is labeled on lima beans. I have two years data that show excellent control of downy mildew at 5.5 fl oz and 8.0 fl oz/A as a preventative application (before disease is found in the field). Ridomil Gold/Copper has a national label now so no 24c label is needed. Headline from BASF is also labeled for downy mildew as well. I have tested it and it has provided good control of downy when applied on a 10 day schedule at 6.0 fl oz /A. It does not give as good disease control as Ridomil Gold/Copper or Phostrol preventatively but the yields have been comparable. It is also labeled for anthracnose which the other products do not control.

Downy mildew caused by Phytophthora phaseoli

Downy mildew on raceme and petiole

Phytophthora capsici on lima bean pod.

Phytophthora capsici will infect lima bean pods as well and can look very similar. P. capsici or lima bean pod rot is usually found in wet low spots in the field. The fungus growth looks more granulated or “pebbly” than downy mildew, microscopic confirmation is encouraged.

Downy mildew on the upper pod and lima bean pod rot on the lower pod. Note the granular appearance of the fungus on the lower pod and the lack of a reddish brown border on the pod infected with lima bean pod rot or Phytophthora capsici.

Vegetable Crop Diseases – September 11, 2009

Friday, September 11th, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Lima Beans
Continue to scout for downy mildew. The recent weather is very favorable for downy mildew. If downy is found apply RidomilGold/Copper, Phostrol or other labeled phosphorus acid (phosphonate) fungicide. If disease has not appeared in the field Headline, Forum or fixed copper fungicide can be applied preventatively in addition to Ridomil Gold/Copper and phosphorus acid fungicides.

Sweet Corn
Field corn is not the only host for the fungus that caused Northern corn leaf blight. I have seen several fields of sweet corn recently with very high levels of infection clear to the top of the plant. Ears from badly infected plants were not filled out and will not be worth harvesting. Northern has been favored by the cooler and wetter season.

Northern corn leafblightTypical large lesion (3-4 inches long) caused by Northern corn leaf blight

Tomatoes
Late blight
is resurging on backyard tomato plantings at the present time. There is nothing besides chlorothalonil and mancozeb for homeowners but late season commercial planting should be protected from late blight with any of the late blight specific fungicides.

Cole Crops
Downy mildew and Alternaria
can be a problem in fall cole crops (cabbage, collards, broccoli, cauliflower, and kale). When the disease first appears apply a fungicide every 7 to 10 days. Quadris, chlorothalonil, Cabrio, Endura (Alternaria only) Maneb, Ridomil Gold Bravo, Switch (Alternaria only), Actigard (downy mildew only) and Aliette (downy mildew only) are labeled for control. For more information on control please see the 2009 Delaware Commercial Vegetable Production Recommendations.

Keep Scouting for Lima Bean Downy Mildew

Friday, August 21st, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Continue to scout fields for downy mildew. The recent hot weather is less favorable but the high humidity and morning fog might counteract the heat and provide conditions for the fungus to survive until the temperatures cool off. Areas that are getting thundershowers should be checked often for downy. See articles in past issues of WCU for pictures and more information (WCU17:22 and WCU17:20).

Lima Bean Disease Update

Friday, August 14th, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Downy Mildew and Lima Bean Pod Rot
Two more fields were identified with downy mildew this week so it is important to keep scouting. Phytophthora capsici was also identified on pods from a field close to harvest. This disease we have named lima bean pod rot. It is found most commonly in low spots in the field. I had talked about it in the article titled Downy Mildew Identified on Lima Beans in WCU 17:20 and have included another picture to help you identify it in the field. There is no effective fungicide control for this disease at the present time. Copper applications may help, but have not been very effective on Phytophthora capsici on other crops. Some field populations of this fungus may be resistant to Ridomil Gold/Copper as we discovered several years ago, so that product cannot be depended on to provide control unless the fungus population is susceptible to Ridomil (mefanoxam).

P. phaseoli on upper pod, P. capsici on lower podDowny mildew on the upper pod and lima bean pod rot on the lower pod. Note the granular appearance of the fungus on the lower pod and the lack of a reddish brown border on the pod infected with lima bean pod rot or Phytophthora capsici.

White Mold
We have yet to see white mold in limas but there is a new fungicide labeled for white mold in lima and snap beans. Omega 500F (fluazinam) from Syngenta, an excellent white mold fungicide that has been labeled in potatoes and peanuts for a long time, is now labeled on beans (snaps and limas). The good thing is that this fungicide is also very effective against downy mildew on limas if applied preventatively although downy mildew is not on the label. I have one year’s test results under heavy disease pressure and it performed very well at the 5.5 fl oz rate. This label was granted after the recommendations book was printed so it is not in the recs. It is the only product that provides control of both white mold and downy mildew. I am going to get another look at it this fall for downy mildew control so I can have two years of data.

Downy Mildew Identified on Lima Beans

Friday, July 31st, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Downy mildew on lima beans was identified this week on the variety ‘Cypress’ near Harbeson in Sussex County. This is pretty early, but the increased rainfall and cooler than normal temperatures in this area were favorable for infection. Not all lima bean growing areas have had the same amount of rainfall, but growers and crop consultants need to be scouting for downy mildew. Last season downy mildew appeared very late and infected only a few fields. Race F of Phythophthora phaseoli was the only race identified in 2006 and 2008. Preventative applications of 2 lbs fixed copper, 2 lbs. Ridomil Gold/Copper, or 3-4 pts Phostrol have provided control of downy mildew in the past. The newest formulation of fixed copper from DuPont is Kocide 3000 and it performs as well as the other formulations of copper at the rate of 1.3 lbs/A. The best controls continue to be Ridomil/Gold Copper or Phostrol, especially when disease pressure is high. Application at flowering or when pods are first forming is recommended if weather is favorable for disease. If disease is present Ridomil/Gold Copper and Phostrol have shown to provide some curative activity if applied when downy mildew is first seen. Ridomil Gold/Copper has a national label now, so no 24c label is needed. Phostrol has a 24c label which needs to be on hand: http://www.rec.udel.edu/update09/Phostrol24c.pdf. Headline from BASF is also labeled for downy mildew now. I have tested it and it has provided good control of downy when applied on a 10-day schedule at 6.0 fl oz/A. It does control the disease as well as Ridomil Gold/Copper or Phostrol preventatively, but the yields have been comparable. It is also labeled for anthracnose which the other products do not control. If soybean rust had become a problem in other legumes it would have been another fungicide in the toolbox for lima beans, since it is also labeled for soybean rust on limas.

Fungicide Rates and Intervals for Control of Downy Mildew of Baby Lima Beans

Fungicide

Preventative

Curative1

High Disease2 Low Disease3 High Disease2 Low Disease3
Ridomil Gold/ Copper 2 lb 2X7 to 14-day interval 2 lb 1X 2 lb 2X7 to 14-day interval 2 lb 1 to 2X10 to 14-day interval
PhostrolFungi-Phite 3-4 pt 1 to 2X7 to 14-day interval 2-4 pt 1 to 2X7 to 14-day interval 3-4 pt 2X7-day interval 4 pt 1X or2-4 pt 2X7 to 14-day interval
Fixed Copper4 2 lb 4X7-day interval(may not control) 2 lb 2 to 3X7 to 10-day interval

Not Recommended

1Curative – when disease first seen, very low incidence, less than 1% of pods and/or racemes infected
2High Disease – conditions very favorable for infection and spread, i.e. ample rainfall, dews, fog and cool temperatures
3Low Disease – conditions less favorable for disease, i.e. low humidity and rainfall and/or temperatures too high (high 80s and above)
4Copper fungicides include Champ DF, Kocide 3000, Cuprofix Disperss and other labeled coppers.

 lima bean pod infected with Phytophthora phaseoli

Downy mildew caused by Phytophthora phaseoli

downy mildew on lima bean racemes

Downy mildew on raceme and petiole

lima bean pod infected with Phytophthora capsici 

Phytophthora capsici on lima bean pod

Phytophthora capsici will infect lima bean pods as well and can look very similar to downy mildew. P. capsici or lima bean pod rot is usually found in wet low spots in the field. The fungus growth looks more granulated or “pebbly” than downy mildew, microscopic confirmation is encouraged.