The Texas Hill Country is known for its beautiful live oak, red oak and even post oak and blackjack oak species. These trees seem to thrive here with little trouble except from people and nature. People affect these trees by building houses, driveways or yards around these fine trees and nature affects them by the drought we are currently in now. Droughts put these trees under significant stress and this stress sets the tree up for the possibility of disease infection. Besides oak wilt we have another problem disease of these oaks called Hypoxylon canker caused by the disease organism Hypoxylon atropunctatum. This disease is found everywhere in abundance but it is not a problem for healthy trees. Stressed trees unfortunately are susceptible to this fungus through wounds and then the disease grows easily in the sapwood. The first symptoms are yellowing and wilting of leaves, and death of top branches of the tree. The fungus is capable of spreading over 3 feet in all directions in a single year from the infection point. Hypoxylon canker is characterized by the large pieces of bark that fall from the tree as it dies because the disease works on the cambium layers that hold the bark in place. Underneath the bark are the fruiting structures of the fungus that are dusty brown spores. These blow from tree to tree to spread the disease further to weak, drought stressed trees.
Before you think all your oaks are going to die please be assured that this disease is not that widespread in our beautiful oaks but it is more of a problem in droughts. Watering all trees but especially oaks in our landscapes a little more this summer will help prevent the stress and consequently the disease.
Friday, May 22, 2009
Where Do Seedless Watermelons Come From?
This past week we had a Vegetable Production Tour around Taylor and Thrall. On this tour we talked about a lot of things including melons and melon production. I have been asked on occasion “Where Do Seedless Watermelons Come From?” and since we are very close to enjoying the first seedless melons of the season I thought we might learn about this great tasting treat.
How do you get seed from a seedless watermelon? Well the process is simple but lengthy taking two generations. First, you need to understand a little about chromosomes, the threadlike bodies that contain genes for development. A regular watermelon has two sets of chromosomes and is called a diploid (di for two). A plant breeder will take a diploid watermelon seed and treat it with a chemical called colchicine. Colchicine will cause the seed to develop a melon with four sets of chromosomes called a tetraploid (tetra for four). This melon is grown out and the seed harvested for the next growing season. This tetraploid seed is planted and begins to grow but the plant is covered with a spun row cover to prevent any pollination so that the plant breeder can pollinate at the right time with a diploid melon variety. These melons will grow and the seed from them will be harvested. The cross of tetraploid plant with a diploid plant results in triploid seed. This plant has three sets of chromosomes and is the “mule” of the watermelon family. This seed when planted will produce a seedless melon meaning it is sterile.
Seedless melons are really a favorite of the urban clientele. They don’t buy grapes with seeds and they don’t like melons with seeds (what do you do with the seeds in a nice restaurant). They are excellent for salad bars and are sold in grocery stores sliced and ready to eat. Seedless watermelon are typically smaller and so fit easily in the refrigerator, another plus for the urban American.
Growing seedless melons are a little different than the typical watermelon. First this seed is very fragile and must be germinated under higher than normal germination temperatures. We will germinate seeds in chambers with 90+ degree temperatures. This forces the seed to quickly germinate and begin to grow versus a cold soil in the field which will slow seed germination enough that most seedless plants won’t make it. Because of its temperamental nature a seedless watermelon is grown as a transplant first and then moved into the field later after getting a good root system established. These seeds cost from 17¢ to 25¢ a piece and growing the actual plant in a pot to be transplanted costs another 10¢ for a total of approximately 32¢ per plant. The germination percentage is low for seedless, around 80%, so that cost can go up even more. It takes about 1500 to 1700 plants per acre or about $450.00 per acre of planted seedless melons, a lot money and still 80 days till harvest.
Seedless have other good traits besides being seedless. They are very productive generally producing more melons than any hybrids if grown properly. They are also disease tolerant plants resisting many of the diseases that other melons quickly die from and seedless are good shippers, holding flavor for a long time.
I mentioned that the seedless is the “mule” of melons, well a watermelon produces both male and female flowers so that we can plant one variety in a field and bees can pollinate with no trouble. A seedless melon produces a male flower that cannot pollinate another melon so to get by this we have to plant seeded melon rows next to the seedless rows to insure good pollination. I have seen mix ups in the field where seedless plants covered 10 solid rows so that the outside two rows were they only ones with melons. Having a pollinator row for seedless is mandatory if you want seedless melons, a fact you should know if you want to try seedless in your garden.
Do You Have Borers or Just a Woodpecker?
The yellow-bellied sapsucker (Sphyrapicus varius), a member of the woodpecker family, is a migratory bird whose summer breeding range includes Texas. The identifying field markings of adult birds are a black crescent on the breast, pale yellow belly, white wing stripe, and a crimson crown. The male also has a crimson chin and throat, distinguishing him from the female whose chin and throat are white.
Although insects make up part of its diet, the sapsucker is better known for its boring of numerous holes in the bark of live trees to obtain sap, the activity from which it derives its name. The yellow-bellied sapsucker is the only member of the woodpecker family to cause this type of injury. More than 250 species of woody plants are known to be attacked. In our area they love our oak species and seem to be particularly fond of red oak and burr oak.
The sapsucker bores neat rows of 1/4-inch holes spaced closely together through the bark of trees along and around portions of the limbs or trunk. As these holes fill with sap the sapsucker uses its brush-like tongue to draw it out. These holes are periodically enlarged and portions of the cambium and inner bark, together with the fresh sap, are eaten.
Puncture wounds and resulting sap flow on branches and trunks of trees are the most obvious symptoms of injury inflicted by the sapsucker.
After repeated attacks on the same area of a tree, large patches of bark may be removed but I seldom see this happen in our area. If this area is girdled, the portion of tree above this point will die. Many small limbs are killed and some- times the trunk is girdled and the whole tree is killed but not often. Sapsucker feeding on shade and ornamental trees leaves unsightly bleeding wounds that attract bees, hornets, and other insects to the sweet, oozing sap.
Early in the spring the sapsucker tests many trees around its selected nesting site by making sample drillings before selecting ones it prefers. These trees, because of quantity or sugar content of the sap, are visited several times a day for the rest of the season and sometimes are used as a food source for several years.
Feeding wounds serve as entry courts for a wide variety of wood decay or stain fungi and bacteria. On high quality hardwoods, sapsucker wounds cause a grade defect called "bird peck" that lowers the value of the trees. Many forest trees are attacked high in the crowns, making light feeding wounds or sample drillings less evident. A condition known as black bark may develop which results from certain fungi colonizing the sap flow and discoloring the bark, and is good evidence that injury exists.
To discourage sapsuckers from feeding on a favorite shade tree, wrap hardware cloth or burlap around the area being tapped or smear a sticky repellent material, such as bird tanglefoot, on the bark. On large acreage or orchards, leave favorite feeding trees of the sapsucker untreated. Birds will concentrate their feeding activities on these favorite trees, which often protects nearby trees from serious injury.
The Migratory Bird Treaty Act and Federal regulations promulgated under its authority prohibit shooting or trapping of sapsuckers. Shooting of this species would be an ineffective control anyway because transient birds tend to replace occasional losses to local sapsucker populations.
Although insects make up part of its diet, the sapsucker is better known for its boring of numerous holes in the bark of live trees to obtain sap, the activity from which it derives its name. The yellow-bellied sapsucker is the only member of the woodpecker family to cause this type of injury. More than 250 species of woody plants are known to be attacked. In our area they love our oak species and seem to be particularly fond of red oak and burr oak.
The sapsucker bores neat rows of 1/4-inch holes spaced closely together through the bark of trees along and around portions of the limbs or trunk. As these holes fill with sap the sapsucker uses its brush-like tongue to draw it out. These holes are periodically enlarged and portions of the cambium and inner bark, together with the fresh sap, are eaten.
Puncture wounds and resulting sap flow on branches and trunks of trees are the most obvious symptoms of injury inflicted by the sapsucker.
After repeated attacks on the same area of a tree, large patches of bark may be removed but I seldom see this happen in our area. If this area is girdled, the portion of tree above this point will die. Many small limbs are killed and some- times the trunk is girdled and the whole tree is killed but not often. Sapsucker feeding on shade and ornamental trees leaves unsightly bleeding wounds that attract bees, hornets, and other insects to the sweet, oozing sap.
Early in the spring the sapsucker tests many trees around its selected nesting site by making sample drillings before selecting ones it prefers. These trees, because of quantity or sugar content of the sap, are visited several times a day for the rest of the season and sometimes are used as a food source for several years.
Feeding wounds serve as entry courts for a wide variety of wood decay or stain fungi and bacteria. On high quality hardwoods, sapsucker wounds cause a grade defect called "bird peck" that lowers the value of the trees. Many forest trees are attacked high in the crowns, making light feeding wounds or sample drillings less evident. A condition known as black bark may develop which results from certain fungi colonizing the sap flow and discoloring the bark, and is good evidence that injury exists.
To discourage sapsuckers from feeding on a favorite shade tree, wrap hardware cloth or burlap around the area being tapped or smear a sticky repellent material, such as bird tanglefoot, on the bark. On large acreage or orchards, leave favorite feeding trees of the sapsucker untreated. Birds will concentrate their feeding activities on these favorite trees, which often protects nearby trees from serious injury.
The Migratory Bird Treaty Act and Federal regulations promulgated under its authority prohibit shooting or trapping of sapsuckers. Shooting of this species would be an ineffective control anyway because transient birds tend to replace occasional losses to local sapsucker populations.
Friday, May 1, 2009
Pecan Nut Casebearer
This is the time of year when we become concerned about pecan nut casebearer infesting pecan nutlets. Casebearer will overwinter in a hibernaculum or cocoon and then break dormancy to begin the process that gets us to this time of year. We are now seeing the moths emerge from this process and it is these moths that will lay eggs that become the first generation pecan nut casebearer. The way we know when the moths are flying is not because we look for the moths laying eggs but that we have installed moth traps in the trees. 
These traps have a pheromone inside the trap that attracts male casebearer moths. We put the traps up in the orchard about a month before we expect to see moths so that we know when the moths begin coming into the orchard. We examine the traps every 2-3 days or 3 times a week and record the number of moths captured and then remove the moths. This record of moth catches help monitor the time moths numbers are highest. Once we capture moths then 7 to 10 days later we should begin to see eggs laid on nutlets. Once eggs are laid it takes 4-5 days to hatch and 1-2 days before they enter the pecan. Scouting is very important to make this program work. This past week I had reports from several commercial growers that they had moth catches in their traps. Following the above schedule we should begin to find eggs on the pecan nutlet about May 8 or 9 and possibly nutlet entry on May 13-15. We look for either eggs or entries till we find 2 or more infested clusters of pecans out of 310, then we spray.
Commercial orchards use chlorpyrifos at 1-2 pints per acre, Confirm, spinosad, Sevin, and Bt for pecan nut casebearer control. Homeowners can use Dipel or Javelin both are organic products with bacillus thuringiensis or Entrust with spinosad which is also labeled organic. Two other products are Sevin or malathion. Follow label directions and be sure to get good coverage, moths tend to work the tree tops as well as the bottom.
Once you know when the casebearer is laying eggs mark your calendar because exactly 6 weeks later you can expect the second generation to show up. Sometimes we don’t treat for the second generation because there just aren’t enough to justify the cost but still scouting is important so that we know. (Thanks to the University of Georgia for great PNC pictures!)
These traps have a pheromone inside the trap that attracts male casebearer moths. We put the traps up in the orchard about a month before we expect to see moths so that we know when the moths begin coming into the orchard. We examine the traps every 2-3 days or 3 times a week and record the number of moths captured and then remove the moths. This record of moth catches help monitor the time moths numbers are highest. Once we capture moths then 7 to 10 days later we should begin to see eggs laid on nutlets. Once eggs are laid it takes 4-5 days to hatch and 1-2 days before they enter the pecan. Scouting is very important to make this program work. This past week I had reports from several commercial growers that they had moth catches in their traps. Following the above schedule we should begin to find eggs on the pecan nutlet about May 8 or 9 and possibly nutlet entry on May 13-15. We look for either eggs or entries till we find 2 or more infested clusters of pecans out of 310, then we spray.
Commercial orchards use chlorpyrifos at 1-2 pints per acre, Confirm, spinosad, Sevin, and Bt for pecan nut casebearer control. Homeowners can use Dipel or Javelin both are organic products with bacillus thuringiensis or Entrust with spinosad which is also labeled organic. Two other products are Sevin or malathion. Follow label directions and be sure to get good coverage, moths tend to work the tree tops as well as the bottom.
Once you know when the casebearer is laying eggs mark your calendar because exactly 6 weeks later you can expect the second generation to show up. Sometimes we don’t treat for the second generation because there just aren’t enough to justify the cost but still scouting is important so that we know. (Thanks to the University of Georgia for great PNC pictures!)
Galls on Oak Trees
I don’t think there is a week goes by that somebody doesn’t call wanting to know what those little balls are on their oak tree how to keep them from killing the tree! How do you tell someone that the damage they see is really not bad at all and in fact these balls are part of the normal eco-system? Well, I can honestly say that most people need more of an explanation than that and here is the answer.
The Mealy Oak Gall has been around as long as the live oak tree. What is a gall, in particular the mealy oak gall? Galls are abnormal swellings of plant tissue that can be caused by insects, bacteria, fungi, mites and nematodes. In our area the galls of most concern are those caused by insects and few by mites. Basically the insect, through many different processes depending on the insect, causes the plant to form or grow tissue that surrounds the insect. As the tissue grows the insect is surrounded and protected within a gall and this gall is the food source for the insect. Once the gall is mature it quits using the plant nutrients but the insect inside will continue to feed through its life stages.
This gall making and insect feeding may sound very harmful to the plant but overall gall-making insects are not considered problems and even some galls are attractive and used in crafts. In the case of the Mealy Oak Gall most people assume that these round galls on the stem are harmful and so want to spray them. Of course it is impossible to get an insecticide to the insect since it lives inside the tree and remember they are not harmful to you or to the tree.
The Mealy Oak Gall is caused by the gall-making cynipid wasp. There are over 1,000 species of gall-making wasps world-wide but in our area this is the primary one. This cynipid wasp has a unique life cycle that includes two generations with one being asexual and one being sexual. The generation we are most concerned with is the asexual when the galls are formed. You can begin seeing them on the stems by late summer and really notice them in late fall. Sometime in January the adults will emerge from these galls and the sexual generation starts but only with a very tiny gall structure.
A second gall-making insect I get lots of calls about is the Oak Apple Gall. This is a really big gall that looks like a green apple on a red oak tree. This gall is basically hollow but if you can imagine as many as a hundred “apples” hanging on your red oak then you understand why people start calling for help. Again this is a harmless pest but the gall makes for really interesting conversation.
Lastly, let me say again that these galls are not a problem. It is not helpful to spray for them or try to inject the tree with some chemical. In fact most gall-making insect populations peak and then begin to disappear. As I said before these galls are just part of the eco-system just like we are!
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