Posts Tagged ‘phytophthora capsici’

Disease ID for Pumpkin

Friday, July 20th, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

I recently wrote an update article about fungicide programs for pumpkin http://agdev.anr.udel.edu/weeklycropupdate/?p=4429. However, because many fungicides are effective on some diseases, but not others, it is important to be able to identify the diseases present in a field as you design your spray program.

Foliar Diseases
The most common foliar diseases of pumpkin are powdery mildew, downy mildew, white speck (Plectosporium), gummy stem blight and anthracnose.

Powdery Mildew

Figure 1a. Powdery mildew sporulation covering leaves and defoliating pumpkin plants.

 Figure 1b. Close up image of a leaf showing the “powdery” white sporulation on the upper surface of the leaf. Note that sporulation is usually seen first on the lower leaf surface. Scout a field by looking at the under surface of 45 old leaves in a field each week. Begin targeted sprays for powdery mildew when it is first observed.

White Speck (Plectosporium)

Figure 2. White speck or Plectosporium on the leaf causes tan spindle shaped lesions which form on the veins and result in distorted leaves. Plectosporium also causes lesions on the fruit (Figure 5).

Downy Mildew

Figure 3. Downy mildew lesions are initially seen on the upper surface as angular water soaked or yellow spots (3a) that are limited by the leaf veins. The angular nature of the lesions is especially evident on the lower leaf surface where sporulation occurs (3b). Look for grey angular lesions on the under surface of leaves after dewy nights. Lesions become necrotic over time.

Anthracnose

 Figure 4. Anthracnose will initially be small tan lesions with darker margins (image courtesy of B. Precheur, Ohio State Univ.). They will expand as they age and damage large portions of the leaf. They may develop small holes in the leaf. Anthracnose also causes lesions on the fruit (Figure 7).

Fruit Diseases
There are several pathogens that cause fruit rot on pumpkin. To manage fruit rot the single most important practice is to follow a good fungicide management program in the field. The same fungi that cause white speck, black rot and anthracnose also cause lesions on the leaves. If the leaves are protected from disease, the fruit will be less likely to become diseased. In addition to protecting fruit from rot, a good spray program will protect “handles” from damage and will maintain foliage health and keep sunscald at a minimum.

White Speck (Plectosporium)

Figure 5. White speck (caused by Plectosporium, formerly Microdochium) causes white or tan “pimples” on the fruit.

Black Rot

Figure 6. Black rot (caused by Didymella bryoniae the same fungus that causes gummy stem blight on the foliage) results in large grey lesions on fruit.

Anthracnose Fruit Rot

Figure 7. Anthracnose fruit rot (caused by Colletotrichum spp.) appears as smaller grey lesions on fruit.

Fusarium Fruit Rot

Figure 8. Fusarium fruit rot (Fusarium solani) causes a relatively dry fruit rot that initially appears as small white or pink spots as in this photo. Eventually however, the lesions may become black or tan because of saprophytic growth.

Southern Blight

 Figure 9. Southern blight on pumpkin fruit (Sclerotinia rolfsii) appears as a fan shaped white growth embedded with small round brown “seeds”.

Phytophthora Blight


Figure 10. A young target shaped lesion (10a) of Phytophthora blight (caused by Phytophthora capsici). Large lesion where fruit was in contact with soil (10b). Close up image of P. capsisi fruit lesion with felt-like sporulation (10c).

Early Season Pythium and Phytophthora Control in Pepper and Tomato Crops

Thursday, April 19th, 2012

Andy Wyenandt, Specialist in Vegetable Pathology, Rutgers University; wyenandt@aesop.rutgers.edu

With the dry spring we’ve had thus far, it’s easy to forget about Pythium and Phytophthora! The same question always comes up about this time of year when growers begin to start thinking about transplanting their tomato and pepper crops. “What should I do to help prevent Pythium and Phytophthora?”. In years past, the answer was simple, apply mefenoxam (Ridomil Gold SL, Ultra Flourish, 4) or metalaxyl (MetaStar, 4). Problem solved, right? In the past, that answer was right, but with resistance development in Phytophthora (P. capsici) to both mefenoxam and metalaxyl, the correct answer isn’t so simple anymore. It’s important to remember that both chemistries will work very well as long as resistance hasn’t been detected on your farm.

How do you know if you have resistance? The easiest way is to follow efficacy. If the chemistries no longer provide the control they once did, then there is a good chance you have mefenoxam-insensitive Phytophthora populations present on your farm. There are also lab services which test for resistance. Remember, once resistance develops it can linger around for a very long time. Therefore, proper crop rotation and resistance management is critical before resistance has the chance to develop.

Our options for pre-transplant applications include a Ranman (cyazofamid, 21) drench one week before transplanting for Pythium in tomatoes as well as Previcur Flex (propamocarb HCL, 28) for the suppression of Pythium and Phytopthora in tomatoes and peppers. Phosphite fungicides, such as ProPhyt and K-Phite (FRAC code 33) can also be applied as a pre-transplant drench in the greenhouse. Additionally, there are a number of biologicals such as Trichoderma, Streptomyces, and Bacillus products which can also be used in the greenhouse to help suppress soil-borne pathogens. Remember, the biologicals need to be applied without conventional fungicides.

At transplanting applications now include Ranman (cyazofamid, 21) in the transplant water or through drip irrigation for Pythium control. There is a section 2ee for the use of Previcur Flex (propamocarb HCL, 28) + Admire Pro (imidacloprid) in transplanting water for Pythium control. Presidio (fluopicolide, 43) now has a label for drip application for Phytophthora control when conditions are favorable for disease development. Additionally, phosphite fungicides, Pro-Phyt and K-Phite (FRAC code 33) can also be applied through drip irrigation at transplanting to help suppress Phytophthora blight. Unlike in the past, there are a number of good options for early season control of these pathogens, it just takes a little bit more planning ahead of time. For further details on use and crop labeled please refer to the specific fungicide label. Remember the label is the law.

Weather Conducive for a Host of Lima Diseases

Friday, September 9th, 2011

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

The recent heavy rainfall from the storms has been very favorable for development of downy mildew. Lima bean fields should be scouted carefully now for the presence of downy mildew as well as white mold. The weather has also raised the possibility of seeing gray mold (Botrytis). Race F of Phythophthora phaseoli was the only race of downy mildew identified in 2006, 2008, 2009, and 2010. Preventative applications of 2 lbs. fixed copper, 2 lbs. Ridomil Gold/Copper, or 3- 4 pts. Prophyte 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, Prophyt, or other labeled phosphonate fungicides and Omega, 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 phosphonate fungicides 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 me can recommend since the fungicide is labeled on lima beans. I have three 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). Omega is not labeled for aerial application, however. Headline from BASF is also labeled for downy mildew. 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 the phosphonates preventatively but the yields have been comparable. It is also labeled for anthracnose which the other products do not control. See the 2011 DE Commercial Vegetable Production Recommendations for more information on fungicides for lima beans.


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 Disease Updates – August 12, 2011

Friday, August 12th, 2011

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

Sweet Corn
With a return to some cooler weather be on the lookout for corn leaf rust on sweet corn. Scout the plantings and if you see rust on plants at the whorl stage or younger, rust could become an issue if the hybrid is not resistant to rust. Rust, when heavy, can affect plant health and reduce ear size. The best control is to plant resistant hybrids, but the strobilurin or triazole fungicide work well. On fresh market corn rust on the husks makes ears unsightly to consumers.

Cucurbits
Cucurbit downy mildew
was recently observed on cantaloupe in the sentinel plot in Newark. These lesions resemble the same symptoms as seen on cucumber but spore production appears to be very sparse. It has not moved to any pumpkin, winter squash or watermelon so far. The susceptible cucumber in the plot is almost totally defoliated.

Lima Beans
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, 2009, and 2010. Preventative applications of 2 lbs fixed copper, 2 lbs Ridomil Gold/Copper, or 3- 4 pts Prophyte 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, Prophyte, or other labeled phosphonate fungicides, and Omega, 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 phosphonate fungicides 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 me can recommend since the fungicide is labeled on lima beans. I have three 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). Omega is not labeled for aerial application, however. Headline from BASF is also labeled for downy mildew. 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 the phosphonates 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 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.

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.

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.

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.