Posts Tagged ‘tomato pith necrosis’

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

Tomato Pith Necrosis Found in Maryland

Friday, June 25th, 2010

Jerry Brust, IPM Vegetable Specialist, University of Maryland; and Karen Rane, Director UMD Plant Diagnostic Laboratory

In the last few days we have received tomato samples that have the same unusual disease called Tomato pith necrosis. Tomato pith necrosis is caused by the soilborne bacterium Pseudomonas corrugata. Pith necrosis has occurred infrequently in Maryland over the past few decades. The disease usually is found in early planted tomatoes when night temperatures are cool, but the humidity is high, and plants are growing too rapidly because of excessive nitrogen application. Once night temperatures warm up, the plants usually outgrow the problem. We have had an early spring, which has allowed many growers to plant their crops 2-3 weeks earlier than normal. We then had cool nights in May and at times high humidity. In the field, diseased plants occur randomly with initial symptoms often being seen as the first fruit clusters reach the mature green stage. Symptoms include chlorosis (yellowing) of young leaves and shoots, followed by wilting of the infected shoots in the upper part of the plant canopy (Fig. 1). This wilting is usually associated with internal necrosis at the base of the stem. Black streaking may be apparent on the surface of the main stem, which often splits (Fig. 2). When the stem is cut open along its length the pith will be discolored, and may have hollow areas (Fig. 3). There is often prolific growth of adventitious roots in the stems with discolored pith, and the stems may appear swollen.

There is not much that can be done for control of pith necrosis. The best practice is prevention by avoiding the use of excessive amounts of nitrogen in tomato, especially early in the season when nights are still cool. Using plant activators such as acibenzolar-S-methyl (Actigard) have resulted in 55% disease reductions, but applications must be started before symptoms appear. There is some evidence that the pathogen may be seedborne, but more research is needed on the epidemiology and management of this disease.

Figure 1. Whole plant symptoms of tomato pith necrosis

Figure 2. Splitting of the main stem and darkened pith caused by tomato pith necrosis

Figure 3. Discolored pith and prolific adventitious root growth cause by tomato pith necrosis