BACTERIAL FRUIT BLOTCH OF WATERMELON

Watermelon bacterial fruit blotch was first reported in North Carolina in 1989. Since then, very few cases have been reported in our state. To the south of us, however, there has been widespread outbreaks of this disease. Therefore, we need to be on the lookout for it.

On watermelon seedlings, symptoms appear as irregularly shaped brown lesions along the midrib that spread to the margins of the cotyledons. These lesions appear water-soaked on the underside of the cotyledons. The lesions can also be seen on the young tree leaves. In the field, fruit blotch infected plants may look healthy. Closer inspection of the plants will reveal small, dark brown lesions that are often bordered by leaf veins or yellow tissue. These lesions will also appear water-soaked on the underside of the leaf. Foliar lesions do not usually cause damage, instead, they serve as a source of infection for fruit. Fruit symptoms show up as dark, gray-green stains or "blotches" on the upper surface of the melon. They initially appear about the size of a quarter and enlarge until the entire melon surface is covered. As the disease progresses, the rinds may split and ooze a sticky, amber colored substance.

The bacteria from infected plants can be spread by splashing rain or irrigation water. It can also be spread by working or handling the plants when wet. Infection can be carried on the seed as well. The bacterium overwinters in plant debris and rinds.

If it is caught early enough and the infection is mall, the disease can be controlled with a weekly copper spray. Other control measures include: work with plants and in fields only when they are dry, avoid overhead irrigation, wash equipment with hot soapy water after leaving an infected field and before moving to other watermelon fields, disk in and destroy infected plantings immediately after the last harvest rotate crops and control volunteer watermelon plants with herbicides.

This disease has caused significant losses to watermelon growers in other areas. As I mentioned earlier, the fruit blotch bacteria can be carried on the seed. This has lead to lawsuits being filed by some growers against some of the seed producers. There is no adequate method of testing the seed for this disease. Therefore, several of the major seed companies have suspended sales of watermelon seed until a reliable method of seed testing has been found. This will most likely result in a shortage of watermelon seed for next year.

Scout your fields regularly and closely. If you suspect that you have watermelon bacterial fruit blotch or any other diseases, feel free to contact me.

SOIL SAMPLING TIME HAS ARRIVED

It's that time of year again. Fall is here and everyone from the farmers to the homeowners are taking their soil samples in for analysis. I encourage you to take your samples now so that you can get your results back in time to plan for the next growing season. We have the soil sample boxes along with the information sheets at our office. You can come in and pick them up here and you can also bring the samples back to us and we will take them to the NCDA lab in Raleigh.

This is the busiest time of the year for the NCDA soil lab. Getting your soil test results will take longer than at any other time of the year. With this in mind, you should expect about 4-6 weeks for your report to arrive.

PREPARING NURSERY PLANTS FOR WINTER

More than one season is usually required to produce a woody ornamental plant. Being able to overwinter nursery plants successfully is essential to producing a marketable crop. Our winters are normally mild, but we can still have cold snaps that can do some serious damage to nursery stock (by serious damage, I mean damage that can reduce marketability or worse). When managing your nursery stock for winter survivability, you need to think in terms of assisting your stock in acclimating for winter and providing protection when the need arises.

By assisting your plants in acclimating for winter, I actually mean eliminate any factors that hinder winter acclimation. Plants need to slow down as winter approaches. Anything that promotes new growth during the last 6 weeks before the first frost should be avoided. New growth during this time period may not harden well enough to survive freezing temperatures and the plants may suffer injury. Practices that promote unwanted growth include late season pruning and fertilizing, avoid these practices during the last 6 weeks before first frost (you may have trouble reducing late season growth if you use slow release fertilizers).

Regular irrigation during the growing season is essential for maximum growth, but it also aids in winter hardiness. If fertilizer has not been released during the summer due to lack of water, it may be released during late season rains that can promote new growth that may suffer from winter injury. In the fall, you will want to reduce the frequency of irrigation, however, you will still want to irrigate regularly and give your plants an adequate soaking at each watering. Plants that dry out in the fall will have less energy storage in the roots and may not have enough energy for bud break and leaf expansion in the spring. If you overwinter your plants in the open, you will need to water them occasionally. You can also increase plant survival in containers if you irrigate them before a cold period.

You may also want to check your crops potassium levels by having your plant tissue analyzed. If the analysis shows that potassium levels are low, you may want to apply a potassium fertilizer. Some reports say that maintaining proper potassium levels will aid winter hardiness.

Even if the crop has adequately acclimated, you may still need to protect it from cold temperatures. Site selection is the primary factor in protecting field grown stock from winter damage. Locate your field grown stock on sites where cold air will drain away from the planting. This means keeping them on high ground and out of low areas where cold air will settle. You may also want to provide wind breaks to prevent air movement and reduce wind burn.

Seedbeds and liner nurseries are subject to frost heave. Plants under these conditions have small root systems and can be forced out of the ground as a result of the freezing and thawing of the soil. You will want to mulch these plantings during the first winter in order to prevent damage from heaving.

Container grown stock is most susceptible to freezing of the root balls. Roots will die at much higher temperatures than above ground portions of the plant. It is important that the root balls of containerized plants are protected from exposure to freezing temperatures. There are several methods of accomplishing this. One practice is to place containers side-by-side, touching one another and then covering the pots with mulch and filling the empty spaces between pots. Further protection can be accomplished by covering these plants with white* plastic film or row cover material.

Some nurserymen construct overwintering structures for this purpose. These structures look like miniature@ greenhouses. They can be constructed by making rectangular, wooden frames and placing them on the ground. Hoops, made out of some type of flexible material such as conduit, heavy gauge wire or pvc pipe, are attached to the frames to support a layer of white* plastic film or row cover. The plants are placed inside of the frame and then the film is pulled over the top of the hoops and fastened down in order to keep the cold air out. If you need to keep the plants covered for more than one night, remember to allow for ventilation during the day. You can do this by simply opening the ends of the structure during the day and closing them back at night. More sophisticated structures will have vents and ventilation fans installed.

Whatever protection method you choose, keep the following in mind. Before you place plants under protection, make sure that the plants have properly hardened. Irrigate them before covering and if you use plastic or row covers, apply a fungicide. Know the species of plant that you are growing, some may need extra protection.

Finally, keep in mind that plants dry out very readily during the winter and this often is the cause of death from cold temperatures. Protect your nursery from prevailing winter winds by using windbreaks. Containerized plants, evergreens especially, need to be irrigated occasionally during the winter. Evergreens will also benefit from some shade to prevent the sun from damaging the leaves after a frost.

If you would like further information concerning overwintering nursery plants, call me. We also have a horticulture information leaflet that gives more detail about constructing overwintering structures. There is also an extension publication titled "Preparing Nursery Plants for Winter", AG-454, that can be purchased for $3.

* The use of clear plastic is not recommended for winter protection. Clear plastic allows too much heat to build up during the day and too much sunlight that can scald plants. Clear plastic also releases heat quickly at night. White plastic maintains a more uniform temperature range.

@ Some nurserymen use regular sized greenhouse frames for this purpose.

PREVIOUS PAGE HOME