News
June 29th, 2009
Vegetable Pest Status Report June 30, 2009
By John Mishanec, IPM Vegetable Program
General Conditions
A storm system parked itself off the coast and has been dumping lots and lots of rain in throughout the region. With the heavy rains come disease problems associated with high humidity. The big news is late blight (LB) on plants sold at the big home and garden stores. Report are coming in from all over NY as well as the whole North East about late blight infested plants being sold to home gardeners. This will undoubtedly impact local commercial grower. It will impact organic growers more so as there are few effective products that will protect your tomatoes and potatoes from the disease.
The big message is to go out and inspect your potato and tomato fields for late blight. It’s what caused the Irish potato famine and can knock down a crop within a week.
- Go to areas of the field where humidity hangs on, along tree lines, low spots, the corner of the field, etc. Look for a large black spot the size of a half dollar, usually with a white ring of spores around the edge of the spot. Also look into the canopy of the plant where spores can germinate on the stems. You will see large black spot on the stem, about an inch long, usually at the axle of where the leaflet meets the stem. Remember, late blight looks like nothing you have seen before. The spots are big. If you find late blight or think you have it, contact your local Cooperative Extension office. We are trying to track the disease as it progresses through the season.
If you deal with the public, and they ask for help identifying problems on their plants, send them to the local Cooperative Extension office. You do not want people bringing infested plants to your farm.
Alert to Potato and Tomato Growers. Late Blight Found in Potato and Tomato
From Meg McGrath and Dr. Tom Zitter, Cornell University and Steve Johnson, University of Maine
Occurrence of late blight this year is unprecedented. So far in 2009 late blight has been detected in SC, NC, VA, WV, OH, MD, DE, NJ, PA, NY, CT, MA, NH, and ME.
This is the fourth year late blight has been seen on LI since 1988, with the earliest previous detection since then being 5 July. There is no record of it being this widespread in the eastern US this early in the growing season. And it has never been seen on tomato plants for sale in garden center stores, which is the main place that it has been found.
This is an extremely destructive disease when not managed, quickly killing foliage and rotting tomato fruit and potato tubers. Late blight was the cause of the Irish Potato Famine.
Likely all tomato and potato crops on LI eventually will be affected this season. All growers should on a weekly schedule both thoroughly inspect their potato and tomato plantings and apply fungicides.
Classic symptoms are large (at least nickel sized) olive green to brown spots on leaves with slightly fuzzy white fungal growth on the underside when conditions have been humid (early morning or after rain). Sometimes the lesion border is yellow or has a water-soaked appearance. Leaf lesions begin as tiny, irregularly shaped brown spots. Brown to blackish lesions also develop on upper stems. Firm, brown spots develop on tomato fruit. Photographs are posted on the web. Contact your local Cooperative Extension office if you find late blight or suspect you have it.
When late blight is found in a localized spot in a field, promptly destroy all symptomatic plants plus a border of surrounding plants to eliminate this source of inoculum. Physically pull and drop affected plants, spray with herbicide, or disk. The herbicides diquat and paraquat are good choices for applying with a hand sprayer. Gramoxone is effective but dangerous; there is no antidote in the event of accidental exposure. When disking is used the crop should first be sprayed with fungicide because of the potential to move spores on equipment especially while driving out of the field, and the equipment should be pressure washed afterwards.
Please refer to this web site for illustrations ( http://vegetablemdonline.ppath.cornell.edu/DiagnosticKeys/TomLeaf/Late_Tom.htm ).
Conventional Fungicides. Begin a fungicide program with products specifically for late blight in this field and other fields near by. These products have translaminar activity and thus provide better coverage than contact, protectant fungicides. A 5- to 7- day spray interval is recommended when weather conditions are wet and cool. It can be extended to 10 days under hot, dry conditions. Alternate among fungicides in different chemical groups (as indicated by FRAC Code) to manage resistance. The late blight pathogen has demonstrated ability to develop resistance; Ridomil fungicides are no longer recommended because of resistance. Include in each application a protectant fungicide like maneb, mancozeb or chlorothalonil, or triphenyltin hydroxide for potatoes. This is important for resistance management and ensuring effective control, and is specified on the label and thus is a requirement. A spray program with just protectant fungicides applied regularly starting before late blight begins to develop can provide adequate control, but this is challenging to achieve when plants are actively growing and conditions are very favorable for disease development, as has been occurring this spring.
Curzate (FRAC Group 27 fungicide) at 3.2-5 oz/A (3.2 oz for potatoes) or Tanos (also contains cymoxanil, active ingredient in Curzate) at 8 oz is a good choice for the first application because these fungicides have some kickback activity, thus they can suppress some established lesions. The maximum kickback is about 2 days when it is cool, declining with increasing temperatures to about zero above 80 F. Cymoxanil has little residual activity, therefore, 5 days later apply another fungicide.
Revus Top (Group 40 + 3) is a new fungicide that has excellent activity for late blight. It gets into plants fast, in about 30 minutes, then slowly moves in the plant providing good residual. It is labeled for use at 5.5 – 7 fl oz. It does not need to be applied with a protectant fungicide. Unfortunately the US inventory of this product has been used up. However, the manufacturer has responded to the situation and prepared a supplemental label for another fungicide, Revus (Group 40), which is not labeled presently for use on tomatoes and potatoes.
Previcur Flex (Group 28) has some systemic activity, which is an important attribute even though it is not as systemic as Ridomil. It was the only fungicide rated good for symptoms on stems and also for protecting new growth in a bulletin from the University of Maine; it is not known how effective many of the other products are on new growth that develops after the application. It was not rated as highly as other late blight fungicides for leaf symptoms (good vs excellent). It is considered a good choice for an application made right before rain. It is rainfast in 30 minutes. It is labeled for use at 0.7-1.5 pt (1.2 pt max for potatoes). According to the manufacturer Previcur Flex provides best control when applied in blocks of 2 applications alternated with 2 applications of other fungicides.
Other fungicides to consider including in the fungicide program are Gavel (Group 22) at 1.5-2 lb, Forum (Group 40) at 6 fl oz, and Ranman (Group 21) at 1.4-2.75 fl oz. Gavel is the only late blight fungicide formulated with a protectant.
Group 11 fungicides (Headline, Quadris, etc) and Group 33 (phosphorous acid) fungicides are not considered as effective for late blight as the other products.
Good fungicide coverage is critical. Pathogen spores can be moved on equipment and workers, therefore spray and work in affected fields last and clean equipment between fields. As soon as harvest is complete disk down field.
Management in organic crops. Apply fungicides preventatively, using a 5-day schedule when conditions are favorable. Copper is effective for protecting a crop, but copper has been found to be ineffective when used as the sole practice for controlling late blight once it has started to develop. Other OMRI-listed fungicides labeled for late blight include Sporatec, Sonata, Serenade Max, and Companion. It is important to scout regularly and promptly destroy affected plants when found to reduce the amount of inoculum in a field. It is recommended that plants with symptoms be physically pulled up plus a few border plants, preferably on a bright sunny day when possible, then tarp the plants; spores will be killed by sunlight and also heat under the tarp. Scout daily thereafter for a few days to see if more plants develop symptoms. Clean after working in infested fields to avoid moving spores on equipment and workers. As soon as harvest is complete disk down field.
Please Note: The specific directions on fungicide labels must be adhered to — they supersede these recommendations, if there is a conflict. Any reference to commercial products, trade or brand names is for information only; no endorsement is intended.
Tomatoes
Again, because of all the rain, bacterial speck and spot is being found in some locations. If you had bacterial problems last year, be especially careful to look for the problem. It can start on one plant or come from a contaminated tray or table in the greenhouse and with the favorable conditions, spread very quickly. I have seen it on small plants in the field. Look for small black or white spots with a black center (birds eye) on the fruit. You will also see many small, black spots on the leaves and stems. The disease spreads easily on equipment, clothing and pruning knives so be very careful in your tomatoes. Copper applications can slow the spread of the disease.
You can obtain more information and pictures at this link
http://vegetablemdonline.ppath.cornell.edu/factsheets/Tomato_Bacterial.htm#Click
Cucumbers and other vine crops
Rain is again the reason for certain diseases being found on crops. Angular leaf spot is a bacterial disease that causes first white spots (about 1/8 – 3/16″ in size) with black margins on the leaves. The tissue in the middle of the spot then dies, dries up and falls away leaving a ragged hole in the leaf. Wet weather and splashing water spread the disease so you will see pockets of the problem on your plant beds. Often when the plants are growing quickly and weather turns dry, the problem will diminish in the field but with wet weather, it spreads quickly and affect many plants.
Here is a link to pictures of the disease:
http://vegetablemdonline.ppath.cornell.edu/factsheets/Cucurbits_Foliar.htm#Click
Also, flooding in a pumpkin or other vine crops is not good as this is the condition that favors phytophthora blight. If it dries out enough, you may want to disk a circle around the low spot in the field to isolate the flooded area. Phytophthora can spread from plant to plant and if you disk a neutral zone, hopefully you will stop the spread of the disease.
Sweet Corn
Hot, dry conditions in late April and early May allowed grower to plant sweet corn earlier than usual. With floating row cover, some of these fields are in full tassel at this point in the season. While pheromone traps have been catching low numbers throughout the region, it is possible to find European corn borer (ECB) feeding damage in this earliest corn. Growers should walk these fields looking for feeding damage on the leaves that are closest to the tassel. Look for small windows in the leaf where the larvae have chewed away the surface of the leaf but not make a hole in the leaf. Occasionally you will find a broken tassel but with the larvae small, this is unlikely. As the ECB larvae get bigger, they will eat bigger holes in the leaves.
Trap Location ECB – NY ECB- IA
Albany Co. North 2 0
Albany Co. South 2 0
Saratoga West 1 0
Saratoga East – -
Washington Co. North 6 -
Washington Co. South 2 -
Kingston 0 0
Orange Co. South 4 6
Orange Co. North 4 2
Scout your field making between 5 to 10 random stops in the field. Look at five plants every time you stop. Keep a running count of how many plants you see feeding damage. With ten stops, you will be looking at 50 plants. If you find over 8 infested plants, you are over threshold (15% at tassel) and the field should be treated. If you are uncertain, look at more plants. Remember looking for something is different from scouting. With scouting, you are randomly evaluating the field for a true level of the pest. When you look for something, you will find it, but you will not have a true picture of what is in the field. You may have found a hot spot or whatever. It is important that you do a systematic and random scouting of a field in order to evaluate if it is economically necessary to treat the field.
Insect pheromone traps are out. This summer, we will list trap catch by location so you can do a better job following insect flights. Even in traps as far south as Orange County, we have caught low numbers of European corn borer (ECB). Corn borer over-winters here in NY and they usually start flying and laying eggs the last week or May or the first week of June.
Potatoes
Potato leafhoppers have arrived via thunderstorms. This is very early. In 2002, the PLH arrived about the same time and pretty much wiped out he organic potato crop. Keep an eye on this. If you have a net, sweep across the potato row ten times and then look what you find in the net. If you have no net, push the vines into the row and shake them plant. You will see the leafhoppers fall to the ground. PLH are small, about 3/16 of an inch in length and bright green in color. They are shaped like an orange slice. Leafhoppers can do more damage than people realize. By the time you see the edges of the leaf turning black, you have already lost up to 40 percent of your yield. Go out and inspect your potatoes today.
Potato beetles (CPB) are laying eggs and in locations further south, the eggs have hatched and larvae are feeding on the leaves. There are 4 stages of larvae. When the larvae get to be around the size of the adults, that you really need to control them before they move into the next generation. If you don’t control them before they move into the 2nd generation, you will be fighting them all summer. Flag 10 locations in the field where you either have just hatched larvae or eggs. Follow these as they grow. When the larvae reach the stage where they are about a quarter inch in length, than make a control application. You may have to come in a couple times in order to get control of the first generation.
For organic growers, Entrust works great against CPB.
Cornell Vegetable Recommends
The online version of the 2009 Integrated Crop and Pest Management Guidelines for Vegetables is now available at http://www.nysaes.cornell.edu/recommends/
June 28th, 2009
Late Blight has been found on tomato 2 retail outlets in Malone–K-Mart and Wal-Mart. K-Mart Garden Center Manager was quick to take action to remove these plants for sale and dispose of them properly. If you have made purchase of tomato plants from these retail locations or in surrounding counties. Late blight has also been found in two Plattsburgh retail stores. Please take the proper precautions for disposal. Late blight will affect tomatoes, potatoes and egg plants. Here are links with more info:
Updates from Cornell on Late Blight
If you have concerns about your tomatoes call our office at 518-483-7403.