by Chuck Bornt, 6/27/22
Those of you that are frequent readers of vegetable newsletters know that over the last bunch of years, we have been battling a new strain or “clades” of Cucurbit Downy Mildew. In the past, we would see it occasionally, but these new clade types have become annual occurrences especially in cucumbers and melons. One of the best ways to stay on top of CDM is to sign up for the Cucurbit Downy Mildew Forecasting System which is free! I’ve been a member since it started and it is a great way to know when CDM is approaching. I have my account set up to notify me if CDM is reported within a 500 mile radius of my home in Rensselaer County.
Unfortunately, I have now received two positive occurrences of CDM – luckily not in NY, but still the earliest reports I’ve gotten since I’ve been registered. The first one occurred about 10 days ago in Salem County, New Jersey, which for our southern counties is not that far away! However, the good news was that transport events or the risk of spread was very minimal due to the hot, dry weather we’ve had. Yesterday, I received the second occurrence of CDM within 500 miles in Lancaster, Pennsylvania. This is concerning as we have confirmed reports on the west side of us and the south. If there is a silver lining, it’s that the risk of spread and transportation of the spores has been very unlikely into our region. That does not mean you should let your guard down or become lax on your fungicide programs! With these reports, I highly recommend that you maintain a protect program on susceptible crops, especially cucumbers and melons. Chlorothalonil (Bravo, Praize etc.) or mancozeb (Dithane) are good choices. However, remember that mancozeb has a 5 day pre-harvest interval so best used on crops that are not being harvested yet. Mixes with copper it will also help on other diseases like Angular leaf spot.
See the note and links below from our vegetable pathologists Margaret McGrath on Cucurbit Downy Mildew. I’ll talk more about symptoms next post.
Cucurbit Downy Mildew already in New Jersey
From Meg McGrath, Long Island Horticultural Research & Extension Center, mtm3@cornell.edu:
Be prepared for another season with downy mildew starting to develop on cucumber and cantaloupe early in eastern NY and Long Island as happened in 2021. Symptoms were seen in southern New Jersey (Salem County) on 6/11/22, which is 5 days earlier than when it was found in that area in 2021, which was followed by early occurrences in eastern NY (7/7/21) and the earliest occurrence on Long Island where records have been kept since 2007 (7/14/21). The pathogen clade (strain) infecting cucumber also infects cantaloupe. The clade that infects squash, pumpkin and watermelon typically appears in the region during late summer.
- Sign up to receive alerts about downy mildew occurring nearby.
- Inspect crops routinely for symptoms. View images of symptoms.
- Routinely check theCucurbit Downy Mildew Forecast websiteto know where the disease is occurring, what crops are affected, and when there is a forecast for pathogen spread to your area.
- Apply protectant fungicides when downy mildew forecast risk is low. Apply targeted fungicides when risk is moderate to high or downy mildew is present in a crop.
- If you see,please report here.
More information about CDM management on Cornell Vegetables website.
Vine Crops: Green and yellow squash harvest is well underway now which means we should be seeing our first Cucurbit Powdery Mildew, especially in yellow squash varieties. I have not seen any yet, but I know it’s out there! Here is a link to our Vegetable Pathologist, Dr. Margaret McGrath’s most recent recommendations for CPM and below for quick reference is what some sample fungicide spray programs could be – remember, these programs would only be for controlling CPM:
Example recommended targeted fungicide programs (there are other good combinations).
Starting with “Week 1” and following weekly applications and including a protectant fungicide with each application (chlorothalonil, sulfur, etc.):
Proline, Vivando, Proline, Vivando, Luna Experience†, Vivando (6 applications total)*.
Proline, Vivando, Proline, Vivando, Procure, Vivando, Procure (7 applications total)*.
Proline, Vivando, Proline, Vivando, Aprovia Top, Vivando (7 applications total)*.
Proline, Vivando, Aprovia Top, Proline, Vivando, Luna Experience†, Procure, Vivando (8)*.
*program has maximum number of applications of Proline and Vivando permitted to a crop.
†Aprovia Top could be used instead of Luna Experience
We also confirmed Anthracnose on melon leaves last week (cantaloupes). This was a problem last year in several plantings and looks like it might be again this year. If you suspect something going on in your melons, please give me a call at 518-859-6213 or send me a picture. If you suspect it, Quadris Opti (azoxystrobin + chlorothalonil) or other Group 11 fungicide (Pristine, Cabrio mixed with a protectant like chlorothalonil) are good choices. Other options are Luna Sensation and Aprovia Top plus chlorothalonil. Organically, copper would be my first choice.
I have also seen my first Gray Squash Bug eggs which tells me that they are also out there and hatching. Look for these masses of copper colored BB’s. Don’t waste money trying to control the adults – target the nymphs (they look like tiny spiders) by flagging a couple egg masses and timing insecticide applications when they hatch. Insecticides include Assail (acetamiprid) which will also control aphids, Endigo (thiamethoxam + lambda-cyhalothrin), Warrior (lambda-cyhalothrin) or other labeled permethrins (will require multiple applications, especially under hot conditions). For organic control, Neemix plus PyGanic is an option. Focus scouting on maxima type vine crops as they tend to be their favorite types(kabocha and hubbard squash, Turks Turban, Big Max type pumpkins etc.).
Now is also about the time many of our pre-emergent herbicides are starting to lose their efficacy. Sandea/Profine can be applied to cucurbits that have at least 2 true leaves, but are not flowering, at 0.5 ounces per acre plus a non-ionic surfactant. This will not control grasses, but will help with things like pigweed, velvetleaf, ragweed (as long as they are small) and yellow nutsedge. And take my word for it – if you use it, don’t go back to the field for about a week or so – Sandea/Profine will cause some stunting and yellowing, especially the growing points, but will grow out of it. Grass control can be obtained by using Select Max, Section or Poast Plus. Click the link to see a table with the post emergent herbicides labeled for cucurbits, rates, surfactants and notes here:
Potatoes: Potatoes have been flying right along, especially if they have been irrigated. The how dry conditions are favoring Potato Leaf Hoppers which can build quickly in fields. If you have a sweep net, the threshold is 1 adult per sweep or when 15 nymphs per 50 leaves are found. Again, there are quite a few insecticides labeled including the pyrethroids like Warrior or permethrin, but multiple applications will be required. Assail, Dimethoate and Endigo will have longer residual and may require fewer applications. Organically, PyGanic plus Surround (kaolin clay) applied multiple times can be used fairly successfully. Don’t forget to scout those bean plantings as well – they are even more susceptible to Potato leaf hopper damage!!!
Eggplant: Do not be surprised if we start to see Verticillium wilt starting to show up early this year. With the hot dry conditions and stressed plants, I think it will be a bad year for this pathogen. Nothing you can really do except to keep the plantings well watered and in some cases, a little supplemental foliar feeding might help – key here is might! As many of you know I’m not a huge fan of foliar feeding, but in times of stress, I do think it has some merit to keep the plant at least moving along in the right direction. Keep an eye on them also for Potato leaf hoppers as I’ve seen high populations damage the plant and set it back some. Pyrethroids (Warrior, Baythroid, Hero) all are pretty effective at controlling leaf hoppers, but again may require multiple applications.
Cabbage and Brassicas: I’m can’t believe the amount of damage I’ve been seeing from Cabbage Maggot in early plantings. Unfortunately, there isn’t much you can do now as the damage is done. I would take note as to where the damage was and if you need to replant brassicas there next year, consider an insecticide as a drench or over the top after planting. I have also seen Imported Cabbage Worm and a small amount of Diamondback damage in some brassicas recently. Of the two, I think DBM is the harder one to control. There are quite a few insecticides labeled including Coragen, Radiant (both offer residual control), Proclaim, pyrethroids like Warrior and a few Bt’s such as Xentari will work.
Sweet Corn: Lots of early plantings are tasseling and even silking. Moth counts for the usual worm pests for the most part have been low or even non-existent. However, I would say that experience has led me to believe that at least one application of something inexpensive like a pyrethroid just as the tassels are emerging is not a bad idea. The timing is critical, especially for European Corn borer control as the one chance you have to get them is when the tassel is emerging from the whorl and starting to open. After that, it becomes harder to target them once they get into the stalk.
Tomatoes: I started to see the first symptoms of Early Blight in a really, early planted field of tomatoes that have a decent fruit set and sized fruit. Chlorothalonil as a preventative is still a good choice followed by tank mixes of chlorothalonil with materials like Revus Tops, Switch, Priaxor, Luna Tranquility etc. However, please pay attention to the labels and try to rotate chemistries which has been made more difficult with all of the pre-mixes that are out there. I will have more information on EB control in the next post. My colleague Teresa Rusinek is also seeing a lot of Bacterial Canker in the Hudson Valley. Many of us have been battling Bacterial Canker for years and at best can hold it at bay for a bit. Cooper applications plus mancozeb starting at planting is the best approach until harvest as the mancozeb has a 5 day Pre-harvest interval. Even some of the copper materials have a 3 day PHI so plan accordingly.