- Author: Mark Bolda
- Author: Scott Stoddard
We haven't spent much time in this space discussing the plant nutrient potassium (K), because my experience here on the Central Coast in berries is that it rarely shows up as a deficiency. Be that as it may, when UCCE colleague Scott Stoddard (UCCE Farm Advisor in Merced County) recently gave a webinar on this very material together with Compass Minerals, I jumped on the chance to learn more about it.
Potassium in the Plant: Potassium varies in plants depending on age and physiological maturity. A good way to check whether plants are getting enough is to take leaf samples. According to the DRIS work in strawberry I did with UCCE Specialist Tim Hartz and Farm Advisor Mark Gaskell, 1.8 to 2.2% K in the leaf prior to harvest, and 1.3 to 1.8% K during harvest indicates sufficiency in the plants. Note that these levels are for whole leaves, not petioles. Leaf concentrations for caneberries are likely to be pretty close to these, but this has not been empirically investigated in California. Of all the nutrients essential to plant growth, the concentrations of K in the tissue are only surpassed by nitrogen. K is all over in the plant, and some 60% of it is found in the chloroplasts. Since plants, as with nitrogen and phosphorous, will mine their older leaves to move these macronutrients to the younger leaves, K deficiency will first show up in the older leaves. Typical symptoms are white speckling and yellowing and necrosis on leaf margins.
The fruit are also a major sink for this nutrient. For example, in strawberry some 3.7 lbs K2O per acre are removed for every ton of fruit harvested (according to the USDA, raw strawberries contain 153 mg of K per 100 g of fruit), meaning that an average crop yield of strawberries of 6000 ten lb crates is removing 110 lbs K2O per acre.
Potassium in the Soil: Availability in the soil of K to the plant is mediated by many factors including cation exchange capacity (CEC), type of clay, amount of exchangeable K, soil moisture, soil pH, temperatures and to an extent the genetics and developmental stage of the plant. Plant available K exists in the soil in three forms: soil solution K (usually 1 ppm – 10 ppm, which is not nearly enough for plants), exchangeable K (the form of K usually measured by soil tests, mostly found in concentrations of 30-300 ppm, 30 ppm being deficient and 300 ppm being high) and fixed, non-exchangeable K (around 1000 ppm). An equilibrium exists between these three forms, meaning that as the easily available soil solution K is taken up by the plant, it is readily buffered (replaced) by exchangeable K, followed by a more slow buffering and replacement by non-exchangeable K. A laboratory soil test for potassium (ammonium acetate test) measures the soil solution plus exchangeable K. However, it is important to remember that a potassium soil test is a useful but imperfect indicator of K availability to plants. There are situations when supplemental K may be needed even when the soil tests high.
Interference by other Soil Cations: The cations magnesium (Mg), calcium (Ca) and sodium (Na) all can all interfere with plant uptake of K by competing for binding sites in the soil. High alkalinity (high pH), calcareous soils can be cause of a problem with Ca, and Scott shares that soil Mg at 10 times the amount of K (converted to millimole equivalents) can be a source of interference problems as well. For example, research by UC Extensionist Specialist Dr. Tim Hartz and UCCE Farm Advisor Gene Miyao in processing tomatoes has found that if K accounts for less than 2% of the soil CEC, yield and fruit color improve from fertilizer K. In soils deficient in K, or in soils where K is sufficient but Mg is elevated, the magnesium can replace potassium on the exchange complex. Tomatoes have yellow shoulders and melons are soft.
That being said, note that most crops are very resilient to wide ranges of nutrient ratios, and in most areas south of the Sacramento Delta, magnesium has no negative impacts on strawberry production, nor is it commonly known to have negative impacts on strawberry production on the Central Coast.
- Author: Mark Bolda
As part of a "Stories from the Field" promotion, UCCE's Jeannette Warnert did a short biography of my professional background. If you are interested in what I used to do, how I got here and what I am doing now, it's all here in a really nicely put together article.
There's even a picture of me from my time in the Peace Corps in Paraguay in the market garden I grew with my good friend Rolando. It's true what it says, the easily identifiable vegetables like lettuce and carrots we never had any problem selling, but man the Napa cabbage we never sold even a single head. Grew really well though.
http://ucanr.edu/sites/FoodInitiative/?story=1501
- Author: Mary Lou Nicoletti, Santa Cruz County Agricultural Commissioner
The Light Brown Apple Moth (LBAM) is present in urban and natural areas of the county, and can easily migrate into agricultural fields. British Columbia, Canada has zero tolerance for LBAM in shipments of plants and harvested crops. Growers whose fruit will be shipped to British Columbia, Canada must sign a Compliance Agreement with the Agricultural Commissioner. One of the critical elements of that Compliance Agreement is visual field scouting for the LBAM.
Visual Field Scouting Requirements:
- Must begin at least 30 days prior to harvesting fruit for export to British Columbia, Canada.
- Must be performed weekly during the harvest season.
- Written records of the scouting must be kept by the grower.
- The scouting must be done by a licensed Pest Control Advisor (PCA) OR an “approved scout”.
Approved Scout:
- A licensed PCA is an approved scout.
- Growers provide the Agricultural Commissioner with the name of their PCA, who will do the weekly scouting.
- The PCA may be unable to perform the required weekly scouting for the grower, due to weather, a recent pesticide application, or simply because he or she is too busy.
- It may be helpful for growers to assign alternate qualified “approved scouts” to ensure the scouting is performed and recorded on a weekly basis.
- Mark Bolda, UCCE Caneberry and Strawberry Advisor, can provide training and an “Approved Scout” certificate to those who attend the training. Mark is holding trainings in May.
- Approved Scout trainings are scheduled to be given at the UCCE Auditorium, 1432 Freedom Boulevard in Watsonville
o May 28 will be in English – 3PM to 4 PM
o May 29 will be in Spanish – 3 PM to 4 PM
Importance:
- Canada is our county's largest trading partner.
- Serious consequences will result if LBAM is intercepted by Canadian officials on a shipment.
- The grower's records will be examined; if the grower has not complied with the terms of the Compliance Agreement, fines can be levied on the grower.
- The entire industry will be affected. Canada could refuse to accept harvested fruit from the County of Santa Cruz or the State of California. This would cause a drop in price received for all growers due to the extra supply of berries in the market.
- Author: Mark Bolda
We proudly announce the posting of our newest addition to the cost and production studies for berries on the Central Coast. Following some extensive review of grower practices, costs and returns, including some seriously close scrutiny and input by local experts, this study on organic fresh market strawberries is now ready.
First go to
http://coststudies.ucdavis.edu/current.php
and then scroll down to organic, fresh market strawberries for Santa Cruz, Monterey and San Benito counties.
- Author: Mark Bolda
- Author: Steven Koike
For fresh market strawberry, damage to the leafy calyx often results in reduced quality and marketability of the fruit. The calyx is made up of the green, leafy sepals that initially surround and protect the young blossom. As the flower transforms into the fruit, the calyx remains intact and becomes the green whorl of leafy material on the top of the fruit. These are also referred to as “caps.”
Damaged calices exhibit various symptoms, including tan to brown discolored tissue, shriveling of the leafy sepals, and eventual drying and death of the calyx tissue. Diagnosing the cause of dry calyx problems may be difficult because such damage could be caused by disease, inherent traits of some cultivars, or calcium deficiency.
Disease: Leaf blotch disease of strawberry is caused by the fungus Zythia fragaria. The disease primarily causes a leaf disease, with symptoms consisting of tan to gray leaf lesions; lesions usually contain tiny dark brown specks that are the fruiting bodies of the pathogen. For coastal California, leaf blotch is an early spring disease that disappears by mid-summer. Fruit calyx tissues can also become infected and develop tan to brown lesions that may or may not have the fruiting bodies (Photos 1 and 2).
Cultivar trait: Dry calyx can also arise from inherent tendencies of certain varieties when exposed to certain environmental conditions. For example, dry calyx was a common occurrence on the first fruit set, early in the year, for the cultivar Camino Real (Photos 3 and 4). Later in the spring, however, Camino Real fruit grew normally and dry calyx disappeared. Interestingly, for this particular variety the dry calyx is not known to occur when it is grown in Mexico.
Calcium deficiency: Dry calyx symptoms can also be associated with nutritional factors. Young foliage having pinched, brown, dead leaf tips exhibit symptoms of calcium deficiency (Photo 5); such deficiency can be confirmed by tissue testing. On such plants, calices can sometimes develop dry, tan to brown tips (Photo 6) that apparently are linked to this calcium problem.
Difficulty in diagnosis: Dry calyx problems caused by disease, cultivar traits, and calcium deficiency can look very similar. Therefore, field diagnosis can be difficult. Leaf blotch disease on calices can be confirmed if fruiting bodies are present in the calyx tissue or if the calyx tests positive when tested in a pathology lab. Dry calyx on cultivars known to develop this problem is likely related to the cultivar itself. If leaves show calcium deficiency symptoms, dry calyx could be related to nutrition. In addition, calices on strawberry plants could simultaneously suffer from multiple causes of dry calyx. Table 1 summarizes these various factors.
Table 1. Summary of possible causes of dry calyx damage
|
|
|
Dry Calyx |
|
|
Factors |
Zythia leaf blotch |
Inherent cultivar trait |
Calcium deficiency |
|
Calices with fruiting bodies |
yes |
no |
no |
|
Foliage with leaf blotches |
yes |
no |
no |
|
Cultivar known to show drying |
no |
yes |
no |
|
Young foliage with deficiency |
no |
no |
yes |
