debor039

Many of you are about to be done with harvest and some may still have a few more weeks to finish this rainy season. This is a reminder for disease management after harvest. The main reason for you to keep your vines clean after harvest is for winter preparation. Grapevines need to store carbohydrate to survive the cold temperature during the winter. If there is not enough foliage on the vine, it may increase the risk of winter injury. The main target diseases are downy mildew and maybe powdery mildew. I do not typically worry about powdery mildew at this late in the season, unless you already have an on-going outbreak that started a few months ago. Downy mildew is common after late-August in our area and severe infection can result in defoliation. Therefore, in a typical year, downy mildew is the one that I would like to control after harvest. Since it will be after harvest spray, you do not need to worry about the PHI (pre-harvest interval). Thus, you can apply a combination of ma...

I received several emails and phone calls concerning spray before the upcoming hurricane Florence. Hopefully, we will have a window of opportunity to apply materials. Looks like we have a break from rain starting tomorrow for maybe 1.5 to 2 days. Here is the list of materials with low PHI (same as the one I posted last month). Just FYI: here are previous posts about... Late season downy management Botrytis gray mold management Once you have about 1.5-2 hours for the materials to dry after application, that will be sufficient for them to stick to the leaf and cluster surface. Good luck!!

At Winchester, the night time relative humidity has been still very high, close to 100%, in nearly every nights in the past three weeks. In addition, we have been observing rapid development of thunderstorms, pretty much every day in the past few days. I know I sound like a broken record, but these conditions favor downy mildew development because downy mildew pathogen prefers to produce spores under dark, humid conditions. Then spores will be spread via rain. At this point, you do not need to worry about downy mildew infection on clusters; however, they can still infect leaves. Often time, you will initially see infection on the top of the canopy because younger leaves are more susceptible than older ones. Losing the top leaves and laterals are not a big deal; however, once the infection gets severe, it can defoliate many leaves rather quickly (as in the picture above), and that can affect maturing process. Knowing how wet this year has been, it is probably wise to be proactive on dow...

In the last several days, the nighttime relative humidity has been very high (>90%) and temperature has been in the upper 60s ~ lower 70s. This condition is favoring spore production of downy mildew. Please check my previous post about downy mildew management.

Just a reminder on downy mildew management: although the month of July was dry until this week, many of us had a very wet early summer that fostered downy mildew development. In addition, during the last several days, the night time temperature was in low 70s and RH was 95-99%, which was an ideal condition for downy mildew spore production. Thus, if you have not, make sure to protect your vines against downy mildew when you have a chance. If you think you have missed the window, we still have some options. We have materials with kick-back activities against downy (Ridomil products (FRAC=4), phosphite (FRAC=P7, Prophyt, Phostrol, etc.). One of two Ridomil product (Gold MZ) has a mancozeb, which has a 66-day PHI, so, unless you have a late season red, you probably need to use the other formulation, which is Ridomil + copper. Both Ridomil and phosphite are good with kick-back, but you probably want to add a protective material to cover both directions. Examples would be captan (FRAC =...

As if almost a week of thunderstorms and rains was not enough, it looks like we are expecting even more rain in the coming week. Hopefully, you had a good protection before the rain, but even if you did, rain more than 1-2 inches can wash the material away from the canopy. Please see the article from Dr. Annemiek Schilder about rain and wash off of fungicide . Her work suggests that although only a 0.04 inch of rain can wash a certain percentage of a material from the leaf, it takes about 1-2 inches to actually having a negative effect on the efficacy since the rate you apply is typically much higher than the threshold for the efficacy of the material. When we have the next chance of application, what material(s) should we apply? I think many of us are about 2-4 weeks away from the bloom, so, the major concern is downy mildew. If you think you have missed the window (i.e., there were more than 2 inches of rain from the last application of a fungicide against downy mildew, or it has bee...

At Winchester, we had 8 hours of wetness observed on last Thursday, then there are several short rains/thunderstorms. Moreover, the night time relative humidity has been fairly high (> 95%) in the past few days. These conditions favors downy mildew development because downy mildew pathogen prefer to produce spores under dark humid conditions. At this point, you do not need to worry about downy mildew infection on clusters; however, they can still infect leaves. Often time, you will see infection on the top of the canopy around this time of the year because younger leaves are more susceptible than older ones. Once infection gets severe, it can defoliate infected leaves. As usual, it is much better and easier to have a preventative program than try to play a catch up game. There are many good protective materials for downy mildew, such as Revus products, Zampro, Forum (Please note that these three share the same mode of action), and Ranman. In our small trial, we found that fixed copp...

I have heard from several growers that they are seeing downy mildew despite the fact that they have not seen much precipitations.  It could happen because of the humidity, especially during the night.  Warm, humid, and dark condition (just like we have been having during the last few weeks) promotes downy mildew pathogen to produce spores. In addition to these conditions, we had lines of rain storms passed in our areas in the past two days. The length of wetness due to these storms were probably long enough for downy mildew pathogen to cause infection. So, just a reminder.  If you have seen downy mildew, and you have not applied any protective material (captan, Revus, even phosphorous acid products) in the past 10 days or so, you may want to consider a rescue application of a phosphorous acid product to reduce the risk of infection that might have happened in the past two days of rains.  (Note: If you are considering harvest in a few days, I would wait until harvest....

On the previous post, I mentioned that "At this time of the season, what we typically recommend is either mancozeb or captan mixed with sulfur to protect young shoots and leaves.  The reason why I typically do not recommend a use of newer materials such as Revus or Phosphite for downy or Luna or Rally for powdery is because we want to keep it for the critical time for cluster infection, which is from bloom to 4-5 weeks after bloom." However, it looks like at out site, the downy mildew pathogen is taking advantage of the weather conditions.  Although our last application of mancozeb and sulfur was only 6 days ago, I noticed that some of older leaves show symptoms of downy mildew (i.e., the infection might have happened prior to the previous application).  At this point, many of leaves look like the first picture, and disease incidence is probably less than 0.5%, thus, it is difficult to find them; however, we came across with a few leaves with clear symptoms as in the...

We had a short shower event last evening; however, it was short and relative humidity did not stay high for a long time.  Thus, it was not a major disease infection event, except, probably downy mildew, since it only take about 90 min under optimal condition. Speaking of downy mildew, we have seen the beginnings of downy mildew in our experimental vineyard. Although our last application of mancozeb was only 10 days ago, rain events and humid nights probably promoted their development. At the beginning, you will see yellow circular discoloration on upper surface of the leaf.  Please note that sometimes insect can cause similar symptoms. However, if you flip over, you will see tiny white growth (please click the picture to access to a higher resolution file).  This won't happen with an insect damage. Please scout your vineyard, and if you see similar symptoms, it is probably a good idea to incorporate some of fungicides with kick-back activity.  In fact, we applied a p...

Since 9/2 or so, we are observing dew events that were wet enough to make our leaf wetness sensor wet almost every night.  Since our sensors were located about the same height as the lower part of the canopy, leaves were probably wet as well.  Each events were about 6-9 hours.  Most of time, temperature was low (in 50F), but sometimes were in lower 60F.  What this condition promote can be downy mildew.  They tend to sporulate under dark condition, and since their spores can swim, these dews probably are enough for them to infect new tissues.  Due to low Brix, many people are tying to hang their berries longer this year.  Please make sure to have some protection on your foliage so that it can help maturation of berries (+ store carbohydrate for the winter!).  If you are concerned about potential effect of spray materials on wine quality, you can aim your sprayer nozzles to upper part of the canopy so that fungicides won't hit the berries.

It looks like we are going to have another wet week... The rain on the 29th was a very short one, but it was enough to make leaves wet for about 10 hours and the average temperature was higher 60F.  It was infection event for downy, black rot, and Phomopsis.  The rain on the 30th was too short for any infection. Once again, the current condition favors development of downy mildew and black rot.  Please do not let something like the picture below happen to you!  (Downy mildew on a cluster, taken from our downy mildew trial.)