Friday, July 23, 2010

Herbicide Damage on Hackberries

The picture on the left taken by Judy Wilson, Extension Support Staff is a branch from a hackberry tree. This tree is located in native prairie in the Golden Plains Area nearby neighbor's field.
The symptom of whitening or bleached effect can occur with chlorophyll-inhibiting herbicides. Some of these herbicides are atrazine or simazine. Other herbicides that can cause this are clomazone. Clomazone is the active ingredient in Command or Commence.
Atrazine is an odorless, white poweder that dissolves in water and is used to control weeds. It is a restricted use herbicide. Simazine is used to control broad-leaved weeds and annuals. It is an off white crystalline compound which is sparingly soluable in water.
All three of these herbicides act in inhibiting photosynthesis. Chlorophyll is a molecule in the leaf that absorbs sunlight. The radiant energy from sun is then synthesised into carbohydrates from C02 and water. If that cycle is interrupted, as it is with these chemicals then this is the specific result based on their chemical make-up.

Monday, July 19, 2010

Ethylene and the Ripening of Tomatoes

Ethylene (C2H4) affects the growth, development and the senescence with all plants as well as tomatoes. It is present in all vegetables and fruits in small quantities as a natural hormone when the fruit or vegetable reaches a mature stage of development. Also, ethylene is used to initiate the ripening process with fruits and vegetables from an external source.

With tomatoes, the ripening process comes to a halt with temperatures above 85 degrees fahrenheit. When ethylene is not present at these high temperatures, tomatoes do not produce lycopene and carotene pigments responsible for color of ripe tomatoes depending on the cultivar. If ethylene were present the tomato would normally start at light green and go to red, pink, yellow or orange, again depending on the cultivar.

So often, we see tomatoes during the heat of July and August that are at full size called a "mature green" and sit on the vine until temperatures begin to cool down at summers end. At summers end all the tomatoes ripen at once. One other point would be the tomato will successfully stay on the vine unless, there are no other environmental stresses that occur in between the ripening stage.

Many fruits produce ethylene in larger quantities when exposed to external sources of ethylene. Some fruits and vegetables are sensitive to the ethylene and can dimish the quality of the produce and reduce the shelf life. Some of these are broccoli, cabbage, cauliflower, leafy greens and lettuce.

Aside from the fruits and vegetables sensitive to ethylene, the following is a list of fruits which naturally produce ethylene: apples, avocados, bananas, melons, peaches, pears and tomatoes.

To learn more about ripening fruits and vegetables, go on-line and read The Ripener Newsletter.

Wednesday, July 14, 2010

Choosing resistant varieties is best to avoid apple scab

The above pictures are from Cornell University Extension. Apple scab can occur on both apple and crabapple trees. In early April and May this fungus starts on the undersides of the newly emerging leaves. The lesions can be olive green and have very indistinct margins that origniate along the veins of leaves. Overtime the lesions can blacken and the leaves yellow and drop. The falling of leaves can occur in early summer.
The fungus that is responsible for this disease is Venturia inaequalis. Like other fungal diseases, Venturia overwinters within infected leaves. Early spring rains splash the fungus spores to the newly emerging leaves. The initial infection begins. A second spore develops producing infection through the summer and fall.
For control, sanitation is a good practice. Rake and destroy all the leaves in the fall. Prune either your apple or crabapple tree in late winter to maintain an open habit. With better air circulation, you are making it difficult for the fungus to infect the leaf surface. If moisture sits on the leaves with a dense tree canopy there is no hope for any quick evaporation of accumulated water on the leaves or even high humidity.
Timing on spraying is critical. Spraying on a regular basis just as flower buds start showing pink. Spray during wet weather by applying fungicides before a prolonged period of wet weather. This may seem an impossible task. However, keep in mind fungicides protect the leaf surface. So, if you misjudge and the weather turns sunny and hot, at least, you were proactive about it. And you need to be proactive about managing this.
The other best control over apple scab is to plant resistant varieties. There are a few apple varieites that are more resistant such as Liberty, Florina and Goldrush. There are a number of others still being tested. If you want crabapples which are highly resistant Redbud, Prairifire, Red Jewel, Ann E., Basakatong, Tea, White Angel, Sargent to name a few. On the other hand, at the other end of the spectrum the cultivars that are most susceptible are Adams, Brandywine, Candied Apple, Indian Magic, Indian Summer, Profusion, Robinson, Snowdrift, Velvet Pillar, White Candle and White Cascade.
Remember resistance does not mean the cultivar can never be infected. It just means that a cultivar has decreased its chances of acquiring apple scab.

Beware of the Tomato psyllids

Tomato psyllids are damaging to tomatoes and potatoes. Leaves on the tops of tomatoes yellow along the midveins and leaf edges. Leaf veins may turn purple. Growth stops while any new leaves remain small, narrow and stand upright producing a feathery appearance. Potato leaves become thickened and curled. Waxy beads of sugary waste from nymphs can be observed on the plants.

The nymphs are a flat yellow-orange discs about a 1/10 of an inch when full grown which sit on the leaves for up to 3 weeks. There can be between 3 to 4 generations of these psyllids in one season.

The damage begins while the nymphs are sitting on the leaves and feeding they are injecting saliva into the leaves which disrupts the plant growth. So leaf curling, color changes and slowed growth begins.

After the nymphs mature into adults after a few days they go from a pale color to gray or black with white bands and markings.

Where do tomato psyllids come from? Psyllids normally occur in southern states. They migrate to Colorado but they spend their winters in the extreme southwest of the United States and Mexico. Migration starts as the spring weather warms. These psyllids can become a pest in greenhouses with tomato and potato production.

Research trials from Colorado State University have found the most effective control comes when using sulfur. Other choices are permethrin/esfenvalerate rated with fair control.

Wednesday, July 7, 2010

Ash Anthracnose

If you have ash trees in your landscape, pay attention during wet springs and summer when there is wet and cool weather. Anthracnose can overwinter on fallen leaves, so sanitation is key as well as pruning out dead limbs. This disease is caused by the fungus Discula species. The spores of this fungus can be carried by wind and splashing water or rain to the new buds expanding in the spring. Usually, this disease does not cause permanent damage to an established tree. With that said, if an established tree is affected by another stress like drought or root restrictions or insect problem then the tree will be less tolerant of this infection.

The leaf spots have an irregular shape and appear brownish in color. The leaves are misshapen or distorted and it starts from the margins and works in. This disease can cause extensive defoliation even in one season which can weaken the vigor of a tree. The lower and inner portions of the tree are affected because the humidity is higher. Moisture is kept under the tree longer. If the tree looses its vigor, a spring fertilization can help the tree regain its vigor. Fungicidal sprays are not always warranted, since this is a seasonal disease. If the ash has this as a recurring problem and wet springs are here to stay for several seasons in Colorado, then fungicidal spray early on at bud break can help protect the young succulent growth.
Cultural controls are always best. Follow proper watering, mulching and sanitation for your ash. You might want to consider deep root feeder to water your trees rather than allowing the sprinkler system hit the bark of the tree while watering the grass. And watering the grass does not supply the tree with adequate water especially in times of drought. The root systems of turf and trees are at different depths. Tree roots or the absorption roots are about 8 to 10 inches below ground and turf can be at 4 to 6 inches below ground and that depends on your watering practices. Consult your Extension Service if you have questions.