PROCESSING CROP UPDATE

TOMATO & PEPPER EDITION

Prepared by:  Janice LeBoeuf, OMAFRA Vegetable Crop Specialist

The Processing Crop Updates are prepared through the season.  Would you like to be added to the e-mail distribution list?
Call me at (519) 674-1699 or email janice.leboeuf@ontario.ca

TomCast DSVs Now Online
Variegated Cutworm
Recognizing Verticillium Wilt in Tomatoes
Soil Sampling for Verticillium and Nematode Analysis
Lots of Aphid-eaters Out There...Spider Mites
Powdery Mildew in Peppers
PMRA Pesticide Re-evaluation Update

TomCast DSVs Now Online

TomCast DSV maps from May 15 onward are now on the Ontario Weather Network website.

To review the program, tomato fields that were planted before May 25 should have their first fungicide application when 35 DSVs have accumulated from the planting date.  Fields planted after May 25 can wait for 45 DSVs to accumulate before their first fungicide spray.  If the DSV threshold (35 or 45) is not reached by July 11 (July 18 for extremely late plantings), make the first fungicide application anyway.  Subsequent fungicide applications should be made when 20 to 25 DSVs (18-20 DSVs for mancozeb) have accumulated since the previous spray date.

You can use the longer spray intervals when you have applied the strobilurin fungicides (Cabrio EG, Quadris Flowable).  Remember to alternate strobilurin applications with other fungicide families.  Note that the active ingredient in Tanos that controls early blight is in the same family as the strobilurins, so don’t rotate strobilurins with Tanos for resistance management (the other active ingredient in Tanos controls late blight).

Growers who have previously applied copper/fungicide combinations for bacterial disease control can restart their DSV accumulations as of the last spray date IF they used a FULL RATE of fungicide at that time.

In areas not covered by the TomCast system, start fungicide applications when first fruits appear and re-spray at 7 day intervals during continuous warm, moist (dews, fogs, or rain) weather or at up to 12-14 day intervals in warm, dry weather if diseases are under control.

Be sure to read the label before applying any fungicide.

Variegated Cutworm

The keys to success when trying to control variegated cutworm in the tomato crop are getting the insecticide to where the worms are and hitting them while they are small.

Anyone who has scouted for variegated cutworm in tomatoes knows that you usually have to burrow right down into the canopy to find these critters – and if it’s hot, they may be hiding in the soil.  You have to be sure that the insecticide is reaching them; otherwise you’re just wasting time and money.

In order to get the spray into the lower canopy, you may need to increase your water volumes.  Label recommendations for water volumes vary considerably.  Ideally, order some water sensitive paper from your sprayer equipment dealer (around $20 for 50 1”x3” papers) and staple, clip, or pin a few within the canopy at different locations before you run the sprayer across.  Of course, you have to do this when the canopy and your gloves are dry, because any moisture will show up on the paper.  Retrieve them afterwards (be sure to wear protective equipment if you were spraying pesticides) and you will see how effective your spray coverage was in different locations in the canopy.  Besides this method, if you are not happy with the control you’ve been getting, try adjusting water volumes (upwards).

Try to apply the insecticide when the cutworms are up in the canopy feeding – early morning or evening while it’s cool.  That’s the best time to scout for them too.  Remember that pyrethroid insecticides lose effectiveness at high temperatures.  If daytime temperatures are high, spray in the evening (when temperatures are below 22°C) or consider another product.

Scouting is part of the second key to success.  Target your insecticide applications to small larvae (less than 1”).  That takes extra work because you will need to spend some time digging into the crop canopy to catch them early.  It’s not an easy job.  Pheromone traps help in determining when to begin intensive field scouting.  Larvae are much easier to find when they are large and have had time to do more damage, but they are very difficult to control, not to mention that they are about to stop feeding and pupate.  At that stage they are finished doing their damage, so there is no point in treating them.

Recognizing Verticillium Wilt in Tomatoes

With the long stretch of dry conditions we experienced, a lot of verticillium wilt symptoms are showing up in tomato fields now.  As the photos below show, the lesions often appear in a V-shape from the tip or edge of the leaf, but you can always find lesions that don’t have that typical appearance.  There is always a lot of yellowing present with verticillium.  Sometimes yellow lesions are present, with no browning.  This helps to distinguish the symptoms from early blight or late blight.  Other organisms will colonize the dead or dying tissue, so you can often see target spots and other riff-raff in the lesions as well.

Verticillium lesions are typically first found on the lower leaves.  If wilting occurs (it often doesn’t), it is sometimes on one side of the plant or one side of the leaf.  As the disease develops, you can look for browning of the vascular tissue in the main stem.  This is easiest to find low on the stem near the soil line.

There is no control for verticillium wilt in-season.  Keep in mind that even though the symptoms can be very dramatic, yield may be unaffected in many cases.  Soil samples can be taken to assess the level of verticillium in the soil.  Usually, a count for plant-parasitic nematodes is done at the same time, as they tend to increase the severity of the verticillium wilt.  If control measures are necessary, fumigation is the usual method.  This can be done the previous fall or in the spring, well before transplanting.  Cultural practices for managing the disease include long crop rotations away from susceptible crops, good drainage, and adequate moisture.

Soil Sampling for Verticillium and Nematode Analysis

Even in fields where plant-parasitic nematodes and verticillium are present, fumigation does not always pay.  Soil samples can be taken to assess the extent of the problem.  The best times to sample are in May/June and in September/October.  Try to sample at the same time of year each time, using the same laboratory, so that you can compare the counts from year to year.  Counts will be lower in the spring than in the fall.

You can use a regular soil probe for sampling, but sample 8-10” deep.  Discard the top inch or two of soil as populations are usually low at the soil surface.  You want the sample to be from the main root zone.  Many soil laboratories as well as the Pest Diagnostic Lab at the University of Guelph provide nematode and verticillium count services.  For more detailed information on sampling, see the OMAFRA infosheet “Nematode Management” on the OMAFRA website.  Go to http://www.omafra.gov.on.ca, pick a language and type “nematode” into the Search box or call the OMAFRA Agricultural Information Contact Centre at 1-877-424-1300 to get a printed copy.

It is important to ship the samples as soon as possible after collection.  They should be stored at 5-10° C and must not be exposed to extreme heat or freezing temperatures.  Do not let the samples dry out.  Live nematodes are required for the count.

Thresholds for verticillium and nematode counts, based on spring sampling:

If the decision is made to fumigate, leave a non-fumigated strip in the field and assess the yield impact at harvest.  Fumigation is expensive and you want to be sure it pays.

Lots of Aphid-eaters Out There…

If you take a good look into the foliage of your fields these days, you may see quite a few interesting insects crawling and flying around.  A lot of these creatures are busy eating aphids.

Watch OMAFRA’s HortMatters newsletter for details on these insects.  The August 17 issue has an article by Kathryn Carter, “Distinguishing Friends From Enemies: Four Fabulous Insects You Want Visiting Your Orchards”.  It talks about aphid-eating insects that may be found in orchards – and other crops, too!  You can also see “Beneficial Insects & Mites” at http://www.omafra.gov.on.ca/english/crops/facts/beneficial.htm.

Here are a few of the beneficials I’ve managed to take photos of lately in tomatoes and peppers:

I’ve also seen lacewings, lady beetle larvae and syrphid fly adults (hover flies) in the last couple of weeks.  In case you don’t get a chance to look at the web-site or other newsletters, here are some photos from the OMAFRA website:                    

Spider Mites

Two-spotted spider mites have been found infesting many tomato fields in the last few weeks.  Look for the mites and their webbing on the underside of older leaves.  They are extremely tiny, so a magnifying glass is necessary to see them clearly.  You can scout for them by tapping the leaves over a white paper and looking for them crawling on the paper.  You may first notice the problem when you see the symptoms of their feeding on the tomato leaves.

Spider mite populations can increase rapidly during hot, dry weather.  In wetter weather, populations are kept in check by rainfall and fungal pathogens that attack the mites.  Predatory mites and insects also reduce spider mite populations.  You may notice that mites are worse along roads and lanes where the crop gets covered in dust.  The dust interferes with the mite predators, allowing the mites to flourish.  Spider mites also produce webs that help protect them from predators, weather, and miticides.

As spider mites are not insects, applications of some insecticides can make the problem worse by killing off the beneficial insects which feed on the spider mites.  Sevin, for example, has no activity on mites, but kills their predators.  Products like dimethoate (Cygon, Lagon) and dicofol (Kelthane) which are registered on tomatoes do have activity on two-spotted spider mites.

Damage moving in from field edge

Leaves damaged by mite feeding.

What impact will spider mites have on the tomato crop?  While they would not be expected to injure the fruits directly, the mite feeding can cause significant defoliation, exposing fruit to the sun and birds and reducing holding ability.  The farther away harvest is, the more potential impact.  If populations are high and we do not get significant rains to wash them off, expect defoliation to proceed from the field edges inwards.  Look at the current condition of the field and the length of time to harvest and decide if early defoliation would be a problem.  As the mites generally move in from field edges, a border spray is often used by soybean growers, who are more used to dealing with spider mites.  Scout to be sure of the extent of the problem.

Pay attention to pre-harvest intervals when using any pesticide at this time of year.  Dimethoate has a 7 day pre-harvest interval on tomatoes and peppers and 3 day pre-harvest interval on eggplant.  Dicofol has a 7 day pre-harvest interval on tomatoes and peppers and is not registered on eggplant.

Spider mite scouting tip:  You can spread the mites by walking through the field.  Scout the areas where you do not see damage first, then the damaged areas, to avoid spreading the mites to new areas of the field.

Powdery Mildew in Peppers

There have recently been reports of powdery mildew infecting peppers in the Leamington area.  It may also be present, but unnoticed in other areas, as it takes close examination to detect this disease in peppers.  The organism that causes powdery mildew in peppers grows within the leaf and produces spores on the underside of leaves.  Although powdery mildew typically appears as a white powdery growth on most plants, it may actually appear brown on pepper leaves.  The upper leaf surface may develop yellow spots, eventually turning completely yellow and dropping off in severe cases.  Symptoms appear on older leaves first.

The pathogen that causes powdery mildew in peppers has a wide host range, which includes tomato, however it has not been found to infect tomato in our growing region.  Powdery mildew found infecting tomato in the northeast U.S. and Ontario has been caused by a different organism.  Yet another organism causes powdery mildew of cucurbits.  These organisms infecting tomato and cucurbits can produce spores on both the upper and lower leaf surfaces.

Powdery mildew of peppers can develop over a wide range of temperatures in low or high humidity conditions.  Due to its wide host range, it can be difficult to control with cultural practices.  It was first identified in the northeastern U.S. in the mid to late 1990s, although it was found in Florida in 1971.  In Florida, California, and other southern areas, it can cause heavy yield losses due to defoliation and the resulting sunscald.

Photos of the disease can be found at http://vegetablemdonline.ppath.cornell.edu/NewsArticles/PepperyPowdery.htm and http://www.avrdc.org/pdf/pepper/powdery.pdf.

PMRA Pesticide Re-evaluation Update

Here’s an update on active ingredients of interest to tomato and pepper growers that are scheduled to be re-evaluated by PMRA in 2005-2009.  Re-evaluations may result in various outcomes such as no change in use, removal of certain uses, restrictions on use, or deregistration of the product.  As each re-evaluation proceeds, there is opportunity for feedback from grower organizations, OMAFRA, and other stakeholders.  This feedback is very important and can influence PMRA decisions.  For more information and updates on pesticide reevaluation, see the PMRA website - http://www.pmra-arla.gc.ca/english/pubs/reeval-e.html.

Tomato and Pepper Pesticides Scheduled for Re-evaluation – 2005-2009