Posts Tagged ‘tomato’

Hot Weather and Blossom End Rot

Friday, June 17th, 2011

Jerry Brust, IPM Vegetable Specialist, University of Maryland;

The extreme heat that just recently ended was exceptionally stressful on plants, especially newly transplanted plants. But even well established plants found in high tunnels or that were planted early in the year were stressed. Tomato plants in a high tunnel I visited had severe blossom end rot problems that are just now becoming apparent. Usually with blossom end rot you get a few tomato fruit that are all of one general size scattered about on plants. This shows that calcium uptake was deficient just as the fruit was developing. Tomato fruit that reaches the size of a dime usually has all the calcium it is going to need and if it does not the cells of the fruit furthest from the stem do not develop normally and collapse as the cells and fruit expands causing blossom end rot. Calcium (Ca) moves to the plant via mass flow, i.e., where dissolved minerals like calcium move to the root in soil water that is flowing towards the roots. If anything interrupts this constant flow calcium deficiency can occur in developing fruit. For different sized fruit to develop blossom end rot there must have been an extended disruption in calcium uptake. This can be seen in figure 1 where several different size fruit all have developed blossom end rot. Figure 2 shows that large fruit on this particular plant developed before there was a Ca interruption, but the fruit a little younger suffered the hot weather induced Ca interruption, with the smallest, youngest fruit suffering the greatest damage. Tissue analysis from this same set of plants showed that calcium was in the high range when the blossom end rot took place, demonstrating the importance of irrigation and water supply to reduce blossom end rot.

Fig. 1 Several fruit of different sizes with blossom end rot

Fig. 2 Older, larger fruit received enough Ca, but younger, smaller fruit did not


Controlling Tomato Bacterial Spot and Speck

Thursday, May 12th, 2011

Bob Mulrooney, Extension Plant Pathologist;

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.


Grafted Vegetables

Thursday, May 12th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Using grafted vegetables for field production is relatively new practice in the United States. However, it is a common practice in Asian countries as well as other areas of the world.

Grafting involves selecting a rootstock that will confer some desired trait, usually resistance to a soil-borne disease. A scion plant is selected, normally the crop and variety with the horticultural traits desired. The scion is grafted onto the rootstock. For example, with tomatoes, a seedling is severed just above the cotyledon. The above-ground portion (scion) of a desired variety for harvest is secured to the root system (rootstock) of the disease-resistant seedling. Once the grafted transplants heal, they can be planted in the field for normal production.

Vegetables that have been successfully grafted include tomatoes, peppers, and eggplants and watermelons, cantaloupes, cucumbers, and other cucurbits.

Grafting can be effective as a non-chemical control method for many soilborne diseases such as Verticillium wilt and Fusarium wilt in tomatoes, Fusarium wilt in watermelons, and root knot nematodes in tomatoes and cucurbits.

Grafting onto vigorous rootstocks can also allow plants to be more stress tolerant because the rootstock has a greater rooting area. This will allow for better water stress and heat tolerance.

Grafting can also improve overall productivity of crops when no disease or stress is present. Again, the vigorous root systems can improve overall nutrient and water uptake and increase fruit yields. In watermelons, rootstocks have been shown to improve fruit quality and holding ability in the field.

Much research is underway on grafted vegetables throughout the region and several growers have started to use grafted plants for production.


Tomato Spotted Wilt Problems in High Tunnel/Greenhouse Tomatoes

Friday, May 6th, 2011

Jerry Brust, IPM Vegetable Specialist, University of Maryland;

I recently visited a grower that grows both tomatoes and bedding plants. The plants are grown in a high tunnel-like setting, i.e., with heat. The grower was having problems in his tomato plants, but not in his bedding plants. The tomato plants looked like they had tomato spotted wilt virus (TSWV). The symptoms were found on most of his tomato plants, which would be unusual, as most of the time only an occassional plant here and there would be infected with the virus. The grower thought that is what he had as did an alert County Educator—and they were right. The grower unfortunaetly had a perfect storm in his operations that produced high percentages of TSWV infection in his tomato crop, but not his bedding plants.

Tomato spotted wilt virus is an obligate parasite; it must have a living host and must be moved from one plant to another by thrips or through cuttings or possibly seed. TSWV is transmitted most efficiently by Western flower thrips (WFT) (Frankliniella occidentalis), and less so by Onion thrips (Thrips tabaci), Tobacco thrips (Frankliniella fusca) and a few other thrips species. It is not transmitted by Eastern flower thrips (Frankliniella tritici).

WFT completes its life cycle in about 10-18 days. Eggs are laid in the leaf or tomato fruit. When WFT oviposit into tomato fruit they often cause a deeper dimple (black arrows Fig. 1) than other thrips species and very often the dimple is surrounded by a halo of white tomato tissue (white arrow Fig 1). This is how I could tell the grower had WFT present at one time (when I visited I could find no live thrips) at fairly high levels by the ovipositioning marks on his tomatoes. Larvae hatch in about three days and immediately begin to feed and in so doing pick up the virus. After four days, they pupate in the soil, and in a little over three days, the pupae become adults. Only immature thrips can acquire the virus, which they can acquire within 15 minutes of feeding, but adults are just about the only stage able to transmit the virus. Adults can transmit the virus for weeks.

TSWV infected leaves may show small, dark-brown spots (Fig. 2) or streaks on stems and leaf petioles (we found one prickly lettuce weed with such a symptom). Growing tips are usually affected with systemic necrosis and potentially stunted growth. Tomato fruit will have mottled, light green or yellow rings usually with raised centers (Fig 3).

Weed hosts function as important virus reservoirs for TSWV and can survive in and around greenhouses or even high tunnels through the winter. Some of these weeds include prickly lettuce, chickweed, (Fig. 4) spiny amaranth, lambquarters, black nightshade, shepherd’s purse, galinsoga and burdock. This grower unfortunately had a good crop of prickly lettuce at one end of his high tunnel.

The grower had been able to control his thrips populations with spinosad, but western flower thrips are notorious for developing resistance and sure enough have developed resistance to this insecticide in many greenhouses. So populations of WFT increased and with the weeds that were around and in the high tunnel some of which tested positive for TSWV, but negative for INSV, it was a perfect scenario for an outbreak of TSWV. I should note here that we tested for both INSV and TSWV on the tomatoes, weeds and impatiens. Only TSWV was found in the tomato and the weeds. No INSV was found in any sample. Although both viruses are transmitted by the same thrips species these viruses tend to infect either bedding plants (INSV) or tomato/pepper plants (TSWV). The grower threw out all his infected tomato plants and is in the process of killing his weeds in and around his high tunnel. He was able to get control of his thrips in his bedding plants using combinations of pylon and pyrethroids. One variety of tomato the grower was growing that did not show any symptoms of TSWV, even though it was right next to the other infected varieties was Mountain Glory.

Fig 1 Tomato fruit with WFT ovipostion marks

Fig. 2 Tomato leaves with TSWV symptoms and positive immunostrip (two black arrows; Agdia, Inc)

Fig. 3 Tomato fruit with TSWV symptoms


Fig. 4 Two common weed hosts of TSWV; prickly lettuce and chickweed


Late April 2011 Late Blight Status

Friday, April 29th, 2011

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

Currently there are a few reports of late blight (caused by Phytophthora infestans) from elsewhere in the United States. In Connecticut late blight was confirmed on tomatoes grown from farmer-saved seed, and on potatoes grown from organic seed pieces (cultivar ‘Australian Crescent’). In Wisconsin, late blight has also been confirmed on potatoes seed. Again, these confirmations are not local; however, increased scrutiny of tomato and potato for symptoms is warranted.

Symptoms on tomato leaves are lesions that initially appear as light green or grey water soaked areas that expand. Sporulation is white to grey on the under surface of the leaf. Infected leaves die. Petioles and stem lesions are dark brown and irregular.

Figure 1. Symptoms of late blight on a tomato leaf and stem (Courtesy of E. Gugino, The Pennsylvania State University).


Early Transplanting of Warm Season Vegetables

Thursday, April 14th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Earliest plantings of watermelons, cantaloupes, summer squash, and tomatoes will begin in the next 10 days. First transplanting of crops such as peppers and eggplant will begin in early May. One of the characteristics that all of these crops have in common is that they are warm season vegetables that are sensitive to cold temperatures, both in the root zone and above ground. There has been a tendency to risk earlier and earlier plantings as growers try to hit the early market. Over the years, many of our early plantings of summer vegetables have suffered because of early cold damage and inadequate provisions to protect plants.

For early transplanted warm season vegetables choose the lightest ground that warms up quickly. Plant higher sections in the field first. Avoid areas that receive any shade from woods or hedgerows. Early fields should be protected from extreme wind and should not have frost pockets. Rye windbreaks planted between each bed are desirable for early plantings because they limit heat transfer by wind. If no rye windbreaks have been planted, then consideration should be given to using row covers to protect the plants – either clear slitted or perforated low tunnels or floating row covers. Even where windbreaks have been used, row covers may be necessary for extremely early plantings.

Lay plastic mulch well ahead of time to warm soil. Black plastic mulch should have excellent soil contact. Firm beds and tight mulch are much more effective in warming soils. Make sure that there is good soil moisture when forming beds and laying plastic because soil water will serve as the heat reservoir during cold nights.

When producing transplants, use larger cell sizes and grow plants so that they have well developed roots in those cells for the first plantings. Large cell sizes will perform better than small cells in early plantings. Careful attention needs to be paid to hardening off warm season vegetable transplants that will be planted early. Gradual acclimation to colder temperatures will reduce transplant shock. Do not transplant tender, leggy plants or plants coming directly out of warm greenhouse conditions for these early plantings.

Watch extended weather forecasts and plant at the beginning of a predicted warming trend. Monitor soil temperatures in plastic beds and do not plant if they are below 60°F. Soil temperature in beds should be measured at the beginning of the day when at the coolest. When soil temperature conditions are not favorable, wait to plant. Avoid planting in extended cloudy periods, especially if plants have come out of the greenhouse after an overcast period. These plants will not perform well. Extra caution should be taken to minimize root injury during transplanting. When transplanting, make sure that there is good root to soil contact and there are few air pockets around roots.

In years with cold, cloudy, windy weather after transplanting, we have had large losses of transplants in the field. It is critical to have warm soil conditions after transplanting to allow roots to grow out into the bed quickly. In cold, cloudy conditions, plants shut down physiologically, little root growth occurs, and the existing roots on the transplant do not function well. If there is any wind, plants lose more water than they can take up and they die due to desiccation. This is accelerated when the sun does come out – the first sunny day after an extended cold, cloudy period is when you will see the most wilting of weakened transplants.

If cold weather occurs after transplanting, warm season vegetables vary in their ability to tolerate adverse weather after being set out. Tomatoes will stop growth but will grow out without much damage once warm weather returns. Summer squash and cucumber transplants may be temporarily stunted but generally grow out of the condition. Watermelons will hold if they have been hardened off properly. Cantaloupes can be stunted if exposed to excessively harsh early conditions. Peppers and eggplants will not put on any root growth until temperatures are warm enough. If stunting occurs on any of these warm season vegetables, you may lose the early advantage you were seeking. In addition, remember that all of these vegetables are susceptible to frost damage and will be killed by a late freeze.


Various End-of-Year Items: Less Stress on Vegetables Now, Root Zone Temperature and Tomato Fruit Ripening Problems

Friday, September 17th, 2010

Jerry Brust, IPM Vegetable Specialist, University of Maryland;

Figure 1 shows part of a tomato field that I wrote about a few weeks ago concerning how environmental stress (high temperatures and drought) on the plants greatly affected plant viability and fruit quality. Figure 2 is the same field today (Sept 22) with new green growth, lots of flowers and fruit, some of which will make it to harvest. This field has not been irrigated for the past 3 weeks and it is still growing well. It is amazing how vigorous the plants are without the stress of the environment and a heavy fruit load. Too often I think growers do not give environmental stress on their plants enough “credit” for some of the problems they see later in the season regarding fruit set and fruit quality.

One of the difficulties I have been having about some fruit ripening problems we see each year in tomatoes is why the problem seems to occur at about the same time of the season regardless of the maturity of the tomato plants (although plants with a heavy fruit load tended to have more problems than those with lighter fruit loads). One thing I was looking at was potassium (K) levels in plant tissue, which were greatly reduced in plants that were having the fruit problems. But why was the K and sometimes phosphorous (P) levels dropping in these plants at about the same time? One possibility I found was that when root zone temperatures (RZT) reached 82o F or greater the plants slowed their uptake of many nutrients including K, P and ,at times, calcium according to leaf tissue analysis. This phenomenon usually occurred earlier in the season and more severely in high tunnel tomato production systems. The problem is that sometimes as the levels of K decreased it was not always correlated with an increase in fruit problems. There appears to be additional factors involved besides lack of some plant nutrients. Would cooling roots somehow help off-set the heating of the root zone and could irrigation water from a well help this? From preliminary studies that I am still working on it appears the answer is no to both. Plots that were irrigated with well water vs. those irrigated from pond water seemed to have a slightly greater reduction in nutrient uptake, even though the RZT drop was greater temporarily.

One other study I worked on this year showed that I was able to reproduce “thrips” or “mite” feeding injury on tomato fruit with no (actually very low) thrips or mite populations being present (Fig 3). This was done by stressing plants that had a heavy fruit load. The more stressed the plants were (including RZT) the more the “thrips damage” showed up. Plants that were not stressed had little or no “thrips damage”; all plants had the same density of thrips and mites on them—very low. What then is causing this damage to tomato fruit? I still do not know. When I talk to hydroponic tomato growers they recognize this damage as nutrient imbalances and not as insect. This would make sense as the plants in the field become stressed the malady suddenly appears. I’ll talk more about this in winter meetings.


Figure 1. Stressed tomato plants, August 


Figure 2. Same plants recovered, September

Figure 3. Damage to tomato fruit usually attributed to thrips or mites, but with no thrips or mites present

September Vegetable Observations

Friday, September 10th, 2010

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Lima Beans
Lima bean harvest is fully underway across the region and the following are some observations in this challenging year. Late May, June, and some early July plantings lost the first set almost completely (heat induced blossom and small pod abortions). The second set is extremely variable and in many fields, economic yields will depend on what happens with the third set. Growers have commented that they are letting fields advance well above the 10% white/dry seed level that is normal for harvest to allow the later set to fill. Some fields are being harvested at the 20-30% dry seed stage (coming from the earlier set). For harvest considerations, it is better to lose a set completely and harvest the later set than to have a bad split set.

There is still considerable dry land lima bean acreage and I am always amazed at how much drought that lima beans can stand without wilting or showing outward water stress. Plants may be smaller but they survive drought and heat very well. Unfortunately, even though lima beans can survive drought, pod set will be limited. Research has shown over and over again that irrigation is necessary to achieve high lima bean yields. In a year such as 2010 where excess heat is also an issue, pod set can be adversely affected, even under irrigation.

We should emphasize again that water is still the most important nutrient for high lima bean yields. In a research plot area where we were looking at residual effects of biofumigant crops and compost this year, we planted snap beans and lima beans in early June as test crops in a dry land situation. After several weeks of drought and heat the snap beans were wilting during the day and were stunted while the lima beans kept on going. To rescue the plots (so that we could get data), we installed drip irrigation between every 2 rows. The snap beans did recover somewhat but with permanently stunted plants, poor bean quality, and a severe split set. In contrast, the lima beans lost the first set but did put on a decent second set and had good plant health and plant size.

Snap Beans
Summer planted snap beans for September harvest are yielding much better than the summer harvested crops. We are seeing yields in the normal 4 ton/A or better range where there was adequate irrigation (compared to summer yields in the 1-2 ton range).

Pickle Cucumbers
Late crops of pickle cucumbers are variable, largely due to stand loss and inadequate water in fields planted during summer high heat periods. In addition, downy mildew has hit a number of later fields adversely, even where fungicides were applied in a timely manner. Pickle harvest should be completed in the next 7-10 days.

I am amazed at how long some watermelon fields have produced this year where attention has been paid to vine health, nutrition, and water. This certainly is the year where you are able to evaluate the yield potential and longevity of main season varieties and effectiveness of pollenizers. On another note, watermelon fields with good weed control (morningglory in particular), had much better later yields.

Tomatoes had a difficult year in 2010 with most fields having much shorter harvest periods due to the extra heat stress. This is especially evident where beds were allowed to dry out at any time during these stressful periods. Somewhat surprising also is the presence of more disease than would be expected in a dry year.

Watch for Tomato Late Blight

Friday, August 20th, 2010

Bob Mulrooney, Extension Plant Pathologist;

Late blight has not made an appearance in Delaware so far this year. Late summer and fall is when we usually see it on home garden and truck crop tomatoes. For late tomatoes continue with Bravo and/or mancozeb as your protectant fungicide and add a late blight specific fungicide if late blight should occur in the region. See the 2010 Delaware Commercial Vegetable Production Recommendations for products and rates.

Some Ugly Tomato Fields

Friday, August 13th, 2010

Jerry Brust, IPM Vegetable Specialist, University of Maryland;

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