Posts Tagged ‘tomato bacterial spot and bacterial speck’

Odd Year for Some Pests in Tomatoes and Cucumbers

Friday, August 10th, 2012

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

This has been a very hot dry summer so far and we would expect to see pests such as twospotted spider mites and their damage to be common, which we have. However, I have been surprised by the amount of worm (Lepidoptera larvae) damage in tomatoes. Usually worms are a problem in a few fields every summer where they do some damage, but the amount of damage they have done in some fields this year is much greater, around 15-20% of harvestable fruit in several instances. The biggest culprit seems to be yellow striped armyworm (YSAW) Spodoptera ornithogalli (Fig. 1). As the name implies the larvae have two bright yellow stripes on the upper part of the worm running the length of its body. The yellow stripe is often flanked towards the inside with black triangular-shaped markings. This worm species tends to feed on the foliage of many plants, but most of the damage I have seen this summer has been on the fruit with little feeding on the foliage. The fruit damage usually appears as surface feeding (Fig. 1) or feeding holes that are very shallow and do not penetrate too deeply into the fruit (Fig. 2). This often leads to a dry type of damage as opposed to the smaller, deeper holes that often lead to a wet rot (Fig. 2). The YSAW overwinters as pupa in the soil and becomes active in late May or mid-June in our area. This year it has become active much earlier than it normally does and has built its population earlier too. We usually do not see this much damage until late August. Management must take place early when larvae are small; once larvae become large they are difficult to control.

 Figure 1. Yellow striped AW and feeding damage on tomato

Figure 2. Yellow striped AW damage to ripening tomato fruit. Dry (yellow arrows) and wet damage.

Another surprise is that bacterial diseases are turning up in many tomato fields. Moist weather and splashing rains are most often needed for spreading bacteria. Maybe the presence of bacteria in the field is not too surprising, but what is surprising is the widespread nature of the bacterial spot, speck and sometimes canker diseases. Most tomato fields I have looked at in the last two weeks seem to have at least some if not a considerable amount of bacterial disease, usually on the lower leaves (Fig. 3) that in some cases has moved up to the pedicels of the fruit (Fig. 4). Infection of the flower or pedicel with bacterial spot is serious, causing early blossom drop (Fig. 5). From the pedicel the next stop for the bacteria, after a heavy thundershower, will be the fruit. A weekly mixture of mancozeb plus fixed copper or ManKocide should help with bacterial spot or speck, but once in the field, bacterial diseases are difficult to control. If a grower has an older tomato field that has bacterial spot in it that field should be plowed under as soon as possible as it will act as a nursery for spreading the disease to the younger tomato fields.

 Figure 3 Bacterial spot or speck on tomato

Figure 4. Tomato pedicels and blossoms with bacterial spot

Figure 5. Blossom drop due to bacterial infection (yellow arrows) and the start of a flower being aborted (red arrow).

The last ‘surprise’ pest has been the seemingly sudden appearance of downy mildew in cucumber fields (Fig. 6). This disease usually needs cooler weather that we have had little of this summer. But on the 21 of July we had a cool wet period when several areas in the mid-Atlantic set a record low for the daily high (77o F). Right after this brief cool down the downy mildew seemed to explode. Many of the cucumber fields I visited in southern and central Maryland that had been harvested at least once had downy mildew. Once it starts it can defoliate a patch of cucumbers very quickly leaving any fruit to sunburn (Fig. 7).

Figure 6. Downy mildew on cucumber leaf

Figure 7. Cucumber plants defoliated due to downy mildew resulting in sunburned fruit

Controlling Tomato Bacterial Spot and Speck

Thursday, May 12th, 2011

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

Tomato transplants with suspected symptoms can be treated with streptomycin (Agri-Mycin 17, Agri-Strep, 25) at 1 lb/100 gallons, or 1.25 teaspoon per gallon every 4 to 5 days prior to transplanting. Additionally, Kocide 3000 (copper hydroxide, FRAC code M1) has a greenhouse label for speck and spot control in the greenhouse. Apply ½ to 1.5 TBSP per 1000 sq ft. every 5 to 10 days. Remember, phytoxicity is an important issue when applying copper in enclosed structures, see label for cautions, restrictions and liabilities. After transplanting, apply Actigard at 0.33 oz 50WG/A (see label for use), or fixed copper (M1) at 1 lb a.i./A plus a mancozeb (Dithane, Manzate, Penncozeb, M3) at 1.5 lb 75DF or OLF, or ManKocide (M1 + M3) at 2.5 to 5.0 lb 61WP/A on a 7 day schedule.

 

Some Ugly Tomato Fields

Friday, August 13th, 2010

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

I have received samples, gotten reports, and have been in some really ugly tomato fields in the past two weeks. The fields consistently have similar appearances where the bottom third or half of the plants have dead, dark brown, often dried-up leaves (Fig. 1). There have been various reasons for some of the dead tissue. In one case plants had Pith necrosis that we talked about a few weeks ago, another field had bacterial spot that was not controlled very well, in another situation mites were at a very high density, but in many situations there was no plant pathological or insect related reason for the terrible looking field. No pathogen could be found in the stems or roots of the plants and only incidental pathogens or insects on the leaves. What seemed to be happening was a rapid decline of the plants over the last couple of weeks. It appears that the stress of this summer is catching up to some fields as they support a heavy fruit load at this time of the season. Additional factors appear to be lower than needed levels of irrigation and possibly the plants are running out of nutrients. It is hard to put a definitive finger on the cause other than the heat and drought seem to be reducing the plants ability to maintain healthy lower foliage. Much of the fruit on many of these plants is still in remarkably good shape although it goes downhill fast (Fig. 2). The bottom leaves on tomato plants are often used to help fill out fruit when times are tough for the plant, so that these leaves become weakened, yellow and very tough and leathery. This situation seems to be occurring here, but at a much accelerated rate of lower foliage decline. In this weather any additional stress on the plant is going to increase the possibility it declines rapidly. I do not have a sure-fire plan to remedy the situation other than to pick off the fruit load as much as is reasonably possible and increase irrigation levels as well as to feed the plants low concentrations of NPK. The plants are probably not going to recover to any great extent until the heat wave ceases, but you can maintain the plants until you harvest the fruit. The most important thing to do if your field looks like Figure 1 is to take plant samples to figure out exactly what you have. Whether it is a plant disease or insect problem or an environmental one, steps can be taken to remedy the situation, but you have to be sure what you are dealing with first.

Figure 1. Tomato field with the bottom half of the plants with dead leaf tissue

Figure 2. Tomato fruit on plants with dead bottom foliage

Seed Treatment and New Selected Fungicides and Bactericides Labeled for Greenhouse Use Tables in 2010 Recommendations Guide

Thursday, April 1st, 2010

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

All seed used in transplant production as well as any transplants brought into the greenhouse should be certified “clean” or disease-free. Important diseases such as bacterial leaf spot of pepper and tomato can cause major problems in transplant production if introduced into the greenhouse. Bacterial leaf spot of pepper and tomato can be seed-borne and infested seed can be a major source of inoculums in the greenhouse and cause problems in the field later in the growing season. As a rule for any crop, any non-certified or untreated seed should be treated, if applicable, with a Clorox treatment, or hot water seed treatment, or dusted to help minimize bacterial or damping-off diseases. For more information on seed treatments for specific crops please see Table E-13 on page E46 in Section E of the 2010 Delaware Commercial Vegetable Production Guide.

An updated table for selected fungicides and bactericides labeled for greenhouse use is available in Section E of the 2010 recommendations guide. The table includes a comprehensive list of fungicides and biological agents approved for greenhouse use. Table E-14 can be found on pages E47-48 of the 2010 Delaware Commercial Vegetable Production Guide.

Tomato Bacterial Spot and Speck

Friday, May 8th, 2009

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

Tomato transplants with suspected bacterial spot or speck symptoms can be treated with streptomycin (Agri-Mycin 17, Agri-Strep, 25) at 1 lb/100 gallons, or 1.25 teaspoon per gallon every 4 to 5 days prior to transplanting. Additionally, Kocide 3000 (copper hydroxide, FRAC code M1), the updated formulation from DuPont, has a greenhouse label for speck and spot control in the greenhouse. Apply 0.5 to 1.5 tablespoons per 1000 sq ft every 5 to 10 days. Remember, phytoxicity is an important issue when applying copper in enclosed structures; see label for cautions, restrictions and liabilities.

After transplanting, apply Actigard at 0.33 oz 50WG/A (see label for use), or fixed copper (M1) at 1 lb a.i./A plus a mancozeb (Dithane, Manzate, Penncozeb, M3) at 1.5 lb 75DF or OLF, or ManKocide (M1 + M3) at 2.5 to 5.0 lb 61WP/A on a 7-day schedule.

Vegetable Crop Diseases

Friday, May 16th, 2008

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

Pepper Phytophthora Blight
For control of the crown rot phase of blight: Apply 1 pt Ridomil Gold 4E/A or 1 qt Ultra Flourish 2E/A (mefenoxam, 4). Apply broadcast prior to planting or in a 12 to 16-inch band over the row before or after transplanting. Make two additional post-planting directed applications with 1 pint Ridomil Gold 4E or 1 qt Ultra Flourish 2E per acre to 6 to 10 inches of soil on either side of the plants at 30-day intervals. Use the formula under “Calibration for Changing from Broadcast to Band Application” on page E6 of the 2008 DE Commercial Vegetable Production Recommendations to determine the amount of Ridomil Gold needed per acre when band applications are made. When using polyethylene mulch, apply Ridomil Gold 4E at the above rates and timing by injection through the trickle irrigation system. Dilute Ridomil Gold 4E prior to injecting to prevent damage to injector pump.

Tomato Bacterial Spot and Speck
Both bacterial diseases can cause serious problems in the field if infections begin in the greenhouse prior to transplanting.
Symptoms of spot and speck look very similar on infected leaves. Lesions are small, circular, blackish-brown and, with time, develop a halo or yellowing of tissue surrounding the lesion. As lesions develop they can coalesce (join together) and can cause premature death. Since sources for these diseases include seed, weed hosts, volunteer plants and contaminated wood (benches) make sure production or holding areas are disinfested, weed-free and clean prior to introducing transplants. Inspect all seedlings prior to transplanting. Infections can occur on all parts of the tomato plant and can easily be spread during transplant production, by transplanting with contaminated equipment, and by workers’ hands. Tomato transplants with suspected symptoms can be treated with streptomycin (Agri-Mycin 17, Agri-Strep, 25) at 1 lb/100 gallons, or 1.25 teaspoon per gallon every 4 to 5 days prior to transplanting. Additionally, Kocide 3000 (copper hydroxide, FRAC code M1), the updated formulation from Dupont, has a greenhouse label for speck and spot control in the greenhouse. Apply 0.5 to 1.5 tablespoons per 1000 sq ft every 5 to 10 days. Remember, phytoxicity is an important issue when apply copper in enclosed structures. See label for cautions, restrictions and liabilities. After transplanting, apply Actigard at 0.33 oz 50 WG/A, or fixed copper (M1) at 1 lb a.i./A plus a mancozeb (Dithane, Manex II, Manzate, Penncozeb, M3) at 1.5 lb 75DF or OLF/A, or ManKocide (M1 + M3) at 2.5 to 5.0 lb 61WP/A, or Cuprofix MZ (M1 + M3) at 1.75 to 7.25 lb 52.5DF/A on a 7-day schedule.

From Andy Wyenandt, Rutgers University