Tag Archives: Flower buds

Risk of Frosts this Week

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The weather forecasts for the coming week show three days with potential frosts. For Wednesday morning, the National Weather Service is forecasting a low of 29F in Winchester and a low of 30F in Tyro. I’m sure other locations in VA are also at risk of frost.

In the Winchester area, apples are 1/4″ green tip with some cultivars showing pink. Peaches are at first pick to some early blooming cultivars having a few open flowers. The phenology in Central VA is a bit more advanced, with peaches having been in bloom for nearly two weeks. According to the critical temperature charts, we can expect a small amount of damage from these temperatures but not a complete crop failure.  So, fingers crossed that it doesn’t get any colder than predicted. However, even if flowers are not killed by the frosts, there is also the risk of russets and frost rings. Temperatures are forecasted to warm up towards the end of the week.

Below are  links for the Washington State University fact sheets (as pdfs) on the critical temperatures for flower buds:

Michigan State University has adapted the WSU critical temperature fact sheets into this easy-to-read fact sheet.

MSU has also put together an excellent set of resources about freezes and frosts in fruit crops.

Additionally, work done by Dr. Steve McArtney (NCSU) and others has shown that applications of Promalin (gibberellin 4+7 plus the cytokinin 6-BA) at 25 ppm immediately following a frost event may help increase fruit set and cropping. In essence, the Promalin sends signals to the developing fruit that the seeds are still intact and growing, even though the frost has killed the embryo. The result is a crop of parthenocarpic (seedless) fruit. This “rescue treatment” is not a full proof way of setting a crop, and it is still unclear under what environmental conditions and for which cultivars it works best. If the temperatures drop much below 28F, each grower will have to make a decision as to whether or not it is worth trying to rescue the crop with Promalin.

You can read more about the “rescue treatment” with Promalin in this Good Fruit Grower article.

Fruit Bud Damage from Cold Temperatures

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Cold temperatures in the winter, such as we’re experiencing over the next couple-few days with a polar vortex can cause damage to plants, people, and livestock. Tmin forecast 1_6_14_midatlanticAt this time of year, fruit buds on our main tree-fruit crops (apple, peach, cherry, and pear) are still in their winter dormant state (endodormancy). During endodormancy, buds have a very low water content and tend to be more cold tolerant. However, absolute lows are not the only factor to consider. If warm temperatures precede a cold spell, then tree buds tend to be less cold tolerant and are more likely to be damaged. There is also considerable variation amongst species and cultivars. For this reason, critical temperature thresholds, like those developed for spring frost damage to flower buds, are not well defined. However, from an ongoing discussion among pomologists in the Eastern part of North America, the consensus seems to be that peach flower buds start to be damaged at -10F and complete crop failure and/or tree loss occurs at -20F. Cherry and plum flower buds are slightly more cold hardy than peach buds and damage will likely occur at -20F. Apple flower buds can withstand temperatures down to -25F. As of now, the forecast for most of Virginia does not show temperatures dropping below 0F. Hopefully, this means that fruit buds in Virginia will not be damaged by the polar vortex.

Plants are not affected by wind chills (plants do not lose heat to the wind). But people and animals will be impacted by the heat loss from the high winds that are accompanying this storm. I’ve seen several wind chill forecasts for Tuesday in the -10 to -20F range. If your pruning crews are outside, make sure they are dressed appropriately for the cold. Also, make sure that your farm animals at least have shelter from the wind. For more information on protecting farm animals and equipment from the cold, read Cory Childs’ (VCE-Warren Co.) blog post from earlier today.

 

 

Potential for Cold Temperature Damage in Northern VA

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The National Weather Service is predicting temperatures to drop to 22F by the morning of April 4 in the Winchester area. For the bud phenology that I’ve seen in the area, we will probably be spared from having very much damage.

Apples are still dormant with a few early blooming cultivars at silver or green tip. Even at green tip, there should only be 10% damage when temperatures drop to 18F. Peaches with a little pink showing may be susceptible to a low level ~10% of damage. Cherries are still in stage 1 or 2, and should be able to withstand temperatures down to 17F with minimal damage. So, fingers crossed that it doesn’t get any colder than predicted. Temperatures are forecasted to be more “spring-like” next week!

Here are pdf links for the Washington State University fact sheets on the critical temperatures for flower buds:

Additionally, Michigan State University has adapted the WSU critical temperature fact sheets into this easy-to-read fact sheet.

MSU has also put together an excellent set of resources about freezes and frosts in fruit crops.