This year we have had what has seemed like an unusually warm winter. In actuality it has been really cool overall with average temperatures in December being 51.3 degrees, in January 50.6 degrees and February being a cold 58.8 degrees. I get a lot of questions about chilling hours and if we have accumulated enough. Stone fruit trees such as peaches develop their vegetative and fruiting buds in the summer and, as winter approaches, the already developed buds go dormant in response to both shorter day lengths and cooler temperatures. This dormancy or sleeping stage protects these buds from oncoming cold weather. Once buds have entered dormancy, they will be tolerant to temperatures much below freezing and will not grow in response to mid-winter warm spells. These buds remain dormant until they have accumulated sufficient chilling units (CU) of cold weather. Almost any variety of stone fruit you buy will have its chilling requirement on the tag. When enough chilling accumulates, the buds are ready to grow in response to warm temperatures. As long as there have been enough CU’s the flower and leaf buds develop normally. If the buds do not receive sufficient chilling temperatures during winter to completely release dormancy, trees will develop one or more of the physiological symptoms associated with insufficient chilling: 1) delayed foliation, 2) reduced fruit set and increased buttoning and, 3) reduced fruit quality.
Delayed Foliation - A classic symptom of insufficient chilling is delayed leafing out. A tree may have a small tuft of leaves near the tips of the stems and have no leaves for 12 to 20 inches below the tips. Lower buds will break eventually but full foliation is significantly delayed, fruit set is reduced, and the tree is weakened.
Reduced Fruit Set and Buttoning - Flowering, in response to insufficient chilling, often follows the pattern seen with leaf development. Bloom is delayed, extended, and due to abnormalities in pistil and pollen development, fruit set is reduced. In many peach cultivars, flowers drop before or around shuck split, but in others such as ‘Jersey Queen’ and ‘Harvester’, buttons form. Buttons result from flowers which apparently have set but never develop into full-size fruit. The fruit remains small and misshapen as they ripen. If you cut these fruit open, the seed is dead.
Reduced Fruit Quality - The effects of insufficient chilling on fruit quality are probably the least discussed but appear to be very common especially in central and south Texas. The effects on leaf growth and fruit set are dramatic but the effects of insufficient chill on fruit quality are subtle, and can occur when other symptoms do not. Insufficient chilling will cause many cultivars to have an enlarged tip and reduced firmness. Furthermore, fruit ground coloration may be greener than usual, possibly due to the fruit losing firmness before the ground color can fully change from green to yellow. The extent of these quality problems depends on the cultivar and the degree of chilling deficiency.
Mean Temperature Model - The mean temperature model uses mean winter (December and/or January) monthly temperatures to estimate accumulated chilling units. The Stone Fruit Breeding Program at Texas A&M University developed a method to estimate chill accumulation which has demonstrated to be accurate for estimating chill accumulation in Texas from the Lower Rio Grande Valley up to the Red River. The coldest month or months are used for the calculation. In low chill regions (regions where average January temperature is 59-63 degrees F) where January represents the dormancy season, January mean temperature is most accurate for estimation. In high chill regions (regions where average January temperature is below 48 degrees F) a mean December-January temperature is recommended. For Williamson County we would use the December-January temperature model.
Also, this method will make it possible for the grower to know, before fruit thinning time, if chill accumulation was sufficient for a given cultivar. If insufficient chilling is suspected for a cultivar, the grower can implement management and marketing strategies to reduce the impact on costs and labor. Furthermore, chemical sprays such as Dormex that help break dormancy are being researched. These chemicals can be used in late January or early February if insufficient chilling is suspected. On the other hand, the expense of a dormancy-breaking chemical can be avoided if the grower knows that trees have received sufficient chill accumulation.
Williamson County Example
Mean December, 2008 temperature is 51.3°F and mean January, 2009 temperature is 50.6°F
Chilling Units = 4280 minus 68.8 X [(Dec. mean + Jan. mean)/2]
Chilling Units = 4280 - 68.8 X [(51.3° + 50.6°)/2]
Chilling Units = 4280 - 68.8 X 50.95
Chilling Units = 4280 - 3505.36
Chilling Units = 774.64
We normally recommend trees with 600 to 800 hour requirements and sure enough we have had enough chilling hours.
Sunday, March 15, 2009
Sunday, March 8, 2009
Time to Get Those Lawns in Shape
With all the warm weather lately people are ready to start fixing up their landscapes and I am right there with them. I always start off like a fireball but like everyone else, come July I am ready for winter again!! But since spring is here let’s talk about lawn care, probably the biggest plant you have in your landscape and certainly the one that takes the most time.
First off, now is the time to get your lawn mower running again. Certainly it needs the perennial oil change and maybe a new spark plug and for sure some new gas. Fortunately gas is cheaper now than last summer. Once your mower is ready you should mow your lawn as short as you can get it. Now this may be messy but mowing it short will help warm the soil and probably more importantly take out a lot of those winter weeds or at least set them back. Some people call the procedure scalping but I don’t see many mowers that can be set low enough to actually scalp a lawn. I just call this a spring clean-up.
Next you will need to fertilize but only if you have bermudagrass or St. Augustinegrass. These two are already trying to green up telling us that soil temperatures are getting warmer by the day. Since they are starting to grow they are the ones that will respond to fertilizer the best and no matter what you hear the fertilizer they need is nitrogen. This can be the hard part because very few stores sell just a nitrogen fertilizer, either organic or inorganic. But fertilizers that have a lot of phosphorus or potassium are not really needed in our soils and can even tie up other nutrients our grasses need. What we need is 1 pound of actual nitrogen per 1000 sq. ft. or in fertilizer terms 7 pounds of 15-0-0 or 5 pounds of 21-0-0 which is a common nitrogen fertilizer. Also at this time you can apply an iron product if you have consistently had problems with yellow St Augustinegrass. Iron sulphate or Ironite can work well to help with this problem caused by our high pH soils in Williamson County.
Now those of you with Zoysia grass or buffalograss need to wait until later in April to fertilize your grasses. Both of these are slower to start in the spring and fertilizing now can only feed the weeds and other grasses in your lawn and not the actual grass you are growing.
Another thing you need to do now is water, although I think you probably already knew that! We are in a severe drought and there is no moisture in our soils for grasses or landscape plants to start growing. It is unfortunate that we have to start off the year watering but if you expect your landscape to be ready when it finally does rain you must water now. What we want is about 4 inches of wet soil. So water until you can push a shovel in about 4 inches easily. If it doesn’t soak in fast enough then turn off the sprinkler and come back in one hour. This has been a real lesson for me this year since I moved from an area with sandy soils to one here with heavy clay. The soil is great here, and very rich but it does take time to water thoroughly.
Lastly I am getting lots of complaints about weeds and weedy grasses. Well those weeds are not summer weeds only winter weeds. They have all sprouted as a result of the rains we got the first of February or were sprouted and waiting on those rains. Now they are taking advantage of an open lawn and great weather. Earlier I mentioned mowing and this is one of the best ways to really help “restrain” these weeds. If you still have too many and want to get rid of them then you can use spot treatments with a dilute Roundup solution or with 20% vinegar just “painting them with a foam brush. If that is too slow then you might try any of the weed control products you can mix up in a sprayer. Be careful though and don’t drift over to trees or shrubs since these could also be damaged. I sure don’t recommend a weed and feed product since I have never seen homeowners be that careful to avoid flower beds and sure enough these products control flowers too!!
First off, now is the time to get your lawn mower running again. Certainly it needs the perennial oil change and maybe a new spark plug and for sure some new gas. Fortunately gas is cheaper now than last summer. Once your mower is ready you should mow your lawn as short as you can get it. Now this may be messy but mowing it short will help warm the soil and probably more importantly take out a lot of those winter weeds or at least set them back. Some people call the procedure scalping but I don’t see many mowers that can be set low enough to actually scalp a lawn. I just call this a spring clean-up.
Next you will need to fertilize but only if you have bermudagrass or St. Augustinegrass. These two are already trying to green up telling us that soil temperatures are getting warmer by the day. Since they are starting to grow they are the ones that will respond to fertilizer the best and no matter what you hear the fertilizer they need is nitrogen. This can be the hard part because very few stores sell just a nitrogen fertilizer, either organic or inorganic. But fertilizers that have a lot of phosphorus or potassium are not really needed in our soils and can even tie up other nutrients our grasses need. What we need is 1 pound of actual nitrogen per 1000 sq. ft. or in fertilizer terms 7 pounds of 15-0-0 or 5 pounds of 21-0-0 which is a common nitrogen fertilizer. Also at this time you can apply an iron product if you have consistently had problems with yellow St Augustinegrass. Iron sulphate or Ironite can work well to help with this problem caused by our high pH soils in Williamson County.
Now those of you with Zoysia grass or buffalograss need to wait until later in April to fertilize your grasses. Both of these are slower to start in the spring and fertilizing now can only feed the weeds and other grasses in your lawn and not the actual grass you are growing.
Another thing you need to do now is water, although I think you probably already knew that! We are in a severe drought and there is no moisture in our soils for grasses or landscape plants to start growing. It is unfortunate that we have to start off the year watering but if you expect your landscape to be ready when it finally does rain you must water now. What we want is about 4 inches of wet soil. So water until you can push a shovel in about 4 inches easily. If it doesn’t soak in fast enough then turn off the sprinkler and come back in one hour. This has been a real lesson for me this year since I moved from an area with sandy soils to one here with heavy clay. The soil is great here, and very rich but it does take time to water thoroughly.
Lastly I am getting lots of complaints about weeds and weedy grasses. Well those weeds are not summer weeds only winter weeds. They have all sprouted as a result of the rains we got the first of February or were sprouted and waiting on those rains. Now they are taking advantage of an open lawn and great weather. Earlier I mentioned mowing and this is one of the best ways to really help “restrain” these weeds. If you still have too many and want to get rid of them then you can use spot treatments with a dilute Roundup solution or with 20% vinegar just “painting them with a foam brush. If that is too slow then you might try any of the weed control products you can mix up in a sprayer. Be careful though and don’t drift over to trees or shrubs since these could also be damaged. I sure don’t recommend a weed and feed product since I have never seen homeowners be that careful to avoid flower beds and sure enough these products control flowers too!!
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