Field Observations

This is our blog of new information and field observations that you may find helpful.

Fall fertilization to improve plant vigor during harvest.

Does starving certain blueberry varieties of nitrogen in the fall help them achieve dormancy? We all know that dormancy is needed for a ‘safe’ response to Dormex – hydrogen cyanamide (HC) but does dormancy not depend more on the temperature and day length than stage of growth? Is reducing nitrogen in the fall effective for creating dormancy? Does it have a negative effect on plant health during the stress of flowering and fruit set?

Last season I experimented a bit with Jewel variety in my ‘evergreen’ section. It is a section where I predominantly have varieties that I keep fertilizing throughout the winter and do not apply HC, The sections that would receive HC later were not fertilized in the fall at all. Since Jewels respond well to HC, I decided to apply it to the plants in the evergreen section as well. Come harvest, those in the evergreen section had retained much of their leaves despite the HC and were more vigorous, producing larger more abundant fruit earlier than the unfertilized Jewels across the aisle. Despite conventional wisdom, I think that we cut off fertilizer too soon in the fall when we are trying to prepare the plants for HC. I observed that the plants being more vigorous and retaining more leaves gave them a physiological edge over those that we normally starve trying to induce dormancy. The stage of growth of each stem of the plant responds differently to HC depending on what stage it is in. For example, if you observe a prima cane flower stalk or new shoot on a ‘Dormexed’ plant, you do not commonly see any damage at rates appropriate for that variety. However the same plant may have HC damage to emerging flower buds. Stage of growth of each plant stem has everything to do with how HC affects a plant.

One year in mid September, I noticed the leaves on my Gulf Coast variety were turning yellow prematurely and dropping (very early but normal leaf abscission) before fall flower buds had a chance to form. To boil it down, I discovered that Gulf Coast was very sensitive to not having enough nitrogen in the leaves causing premature leaf drop. Linking the experience with Jewels last year with that fact about Gulf Coast, it seems likely that we need adequate nitrogen in the leaves during the fall to prevent leaf drop in varieties like Jewel and that starving them is a mistake resulting in lower yields due to less bud formation and less photosynthetic area during flowering and fruit set. One UF study were nitrogen was traced in the plant through the season implied that plants utilize Nitrogen already stored in the tissues first during the spring. This further supports the hypothesis that it is better to have a healthy level of Nitrogen in the plant than to try to use a deficiency to induce dormancy. Better to wait for some chilling… even if it comes in January.

Recommendations for growing blueberry plants in Florida

Whether you are a commercial blueberry grower or a homeowner just wanting to grow your own blueberry plants, here are some basic guidelines to follow in choosing where and how to plant.

Site selection and preparation: The old adage regarding blueberries goes that there are three things most important to growing blueberries: pH, pH and pH. Needless to say that if the pH of your soil, substrate (i.e.,pine bark) or irrigation water are not the right pH (between 4.5 and 5.5) your planting will not thrive unless you take steps to adjust the pH for your situation. Florida growers who have soil with low organic matter or high pH, typically windrow pine bark into planting beds essentially creating artificial soil. This method commonly used by many commercial Florida growers is somewhat expensive. However many of Florida’s native soils are quite adequate for blueberries. In fact several species of native wild blueberries thrive in certain Florida ecosystems.

Blueberry plants also prefer soils with at least 2-3% organic matter. Soils with inadequate organic matter can be amended by mixing in peat or pine bark which requires less bark than pure bark beds. Good native soil for blueberries would typically be found adjacent to swamps or as pine flatwoods with a high water table and muck soils (spodic soils) that can be bedded for drainage. The only other caveat associated with site selection would be pH of the irrigation water. Typically water obtained from a shallow well or surface water is more acidic however the calcium bicarbonates dissolved in water from deep wells slowly raises the pH of the soil creating an inhospitable environment for blueberry plants. This can be mitigated by acidifying the water or more simply by periodically spreading granular sulfur to the soil surface.

Sivanto- Group 4D insecticide may be very useful during blueberry flowering when they are particularly susceptible to Flower Thrips.  Use of insecticides during bloom puts bee pollinators at risk however the Sivanto label under “Environmental Hazards/Non target organisms” states that Sivanto has no contact effect on bees and no effect on colony development. In our situation of the mix of flowers/thrips and pollinators this is a bonus for Florida Blueberry Growers. If used at 9 oz/ac, it can be applied 3 times per crop cycle and could be useful to add to the arsenal of thrip active insecticides to delay resistance in the neo-nics – group 4A (Assail) and spintorams-group 5 (Delegate). It is possibly as safe and likely more effective than Malathion since it is translaminar. Foliar feeding Chili Thrips have required constant spraying of Blueberries in Central Florida during the summer increasing the potential for resistance of our most effective labeled insecticides.During the summer Chili Thrip season in 2015 we applied Sivanto once with adequate but not spectacular results. It did not seem to have a long residual so we need some additional testing for confirmation.
We sprayed Sivanto on Flicker in early January 2016 when I discovered high numbers (5-15) of Flower Thrips per flower. After re-sampling the following week, Sivanto seemed to have done a good job wiping them out (none found in limited sampling).
In addition on my Dormexed field where I had a significant Indian Wax Scale infestation, I sprayed about a gallon of spray oil mixed with Sivanto banking on the label statement for scales on other listed crops and the fact that such little oil (2% in 50 gal/ac) it would be adequate coverage considering that I sprayed them after defoliating them with Dormex. Upon inspection 2 weeks later, the IWS seemed to be dead or dying (no longer ‘pink’ underneath). I’ll keep an eye on them to see how much residual or recurrence I get in the months to come but I think it may be effective with IWS also.

Labeled rates were adhered to for each of these applications and applied in 50 GPA water.

Low chilling has caused sporadic flowering of some varieties. These flowers will allow flower thrips to get a foothold in your field and be able to increase rapidly when the main bloom comes. Begin to monitor any flowers for thrips and spray Delegate as needed at night if you have any bees working the field. Failure to control flower thrips will result in russetting or softening of the fruit.

Planning your variety mix is one of the most important things that you can do to insure your blueberry farm’s success. To consider which varieties will work best for you should consider these factors:

• Your proposed operation type: i.e. Commercial pick, door yard (home garden), U-pick, etc.
• Horticulture: Use of hydrogen cyanimide or evergreen. Your soil type: pine bark, native soil.
• Row configuration: Conventional, high density, machine harvest.
• Climatic Zone location: Important variety characteristics: Harvest window (currently the most important for commercial farms), yield and consistency of yield year to year, fruit qualities, plant disease tolerance, and plant vigor.
• At present the earliest varieties are Flicker, Chickadee, Kestrel, Winter Bell, and Spring High. Arcadia, Endura and Avanti have also been released and are available however there is limited grower experience with them to date.
• Results from farm to farm vary and each variety has its strengths and weaknesses. For example: Flicker, although very early is no longer recommended due to susceptibility to Anthracnose stem blight.

Florida Blueberry Nursery provides University of Florida and our first patent pending variety ‘Winter Bell’ for Central Florida and similar climactic zones. This is a result of 13 years of yield testing University of Florida and our in house breeding selections to determine what works best for our operation in Winter Haven. Fruit quality, plant vigor and disease tolerance are important however our primary criteria has been to select for seedlings that peak when the price in the Florida market window is also peaking. As competing blueberry producing regions such as Chile and California target our window as well as increases in Florida acreage, FOB fruit prices even in the early window will be increasingly challenged. As returns are diminished by competition, it will be critical to keep costs as low as possible to maintain profitability. One of the areas of high cost for us is harvest labor so we have begun to prepare for this by beginning to select for variety characteristics allowing for machine harvestable fruit.

There are however, still differences in how each variety performs under different climactic and environmental conditions. Unfortunately, many farms experience different results within the same locale. That means producing high quality berries that peak in conjunction with the highest market price for Florida blueberries.

As there will always be challenges, we at Florida Blueberry Nursery will be constantly looking forward for opportunities to meet those challenges.