I'm following up with a quick industry update on the use of preharvest products ReTain and Harvista during drought conditions. I said that I would share insight from another growing region and I spoke with a contact at Cornell, Craig Kahlke. Craig works on fruit quality management and his recommendations come from experiencing drought conditions several times over the last few years. They are experiencing drought conditions again this year too. I greatly appreciate his time and valuable experience he shared with our industry.
- Plant growth regulators like ReTain and Harvista are expected to be less effective at delaying maturity progression than usual.
- If you are accustomed to using these products for labour management then consider your approach in case they are ineffective at delaying maturity this year.
- The products will be relatively ineffective at trying to hang fruit for longer to get better size and colour.
- We should be on high alert for preharvest fruit drop and consider using ReTain or Harvista for stop-drop management if signs of fruit drop begin.
- Although the maturity might not be delayed, the stop-drop action is worthwhile to buy time to pick fruit before they fall.
- Please note that once preharvest fruit drop begins, it can worsen very rapidly within a few short days. Act quickly on blocks if drop begins.
- We also shouldn’t mistake fruit drop for push-off fruit that have broken or missing stems (which is not ethylene driven). Fruit falling due to ethylene production have stems with clean and flat stem surfaces. ReTain and Harvista will only prevent fruit drop associated with ethylene.
Figure 1. Fruit falling off due to ethylene production has a stem and a flat stem surface. Consider stop-drop products if early signs of fruit drop begin.
Plant Growth Regulators
- If no ReTain or Harvista are applied, then early ethylene production in fruit is common during drought conditions.
- Growers waiting for size and colour applied plant growth regulators, but it didn't delay harvest much. The main benefit of the products during a drought year is to hold back ethylene to stop fruit drop.
- Honeycrisp is prone to preharvest fruit drop and it is a big concern during a drought year. Based on our weather conditions they suggest we could see fruit drop on Honeycrisp from drought stress. In their experience significant drop can occur over the span of a few days so try to catch it early in the process.
- The recommendation is to use 1/3 rate of ReTain on Honeycrisp to prevent drop at 2 weeks before harvest. It won't delay harvest or colour much.
- Harvista is a good option if available. It will kick into action faster than ReTain for stop-drop control. In that case you can wait until you're starting to see drop and then use it. Likely it will be applied earlier than usual. Monitor closely and go early before much drop. It may hold back colour a bit.
- Regardless of drought, they always recommend ReTain or Harvista for Gala going into long term storage because without it there is a higher incidence of turning brown. They do ½ rate ReTain at 3 WBH and 1/3 rate ReTain at 1 WBH.
Disorders/Quality
- They received 1 inch of rain recently during the drought this year and experienced fruit cracking.
- In drought conditions they are still benefitting from good colouring weather. But this may vary depending on the level of tree stress.
- Bitter pit is a higher risk in a drought year.
- Calcium fruit sprays have been especially important this year.
- Summer pruning might have contributed some benefits by removing competition with shoots.
- If you are concerned about a particular block, there is a passive prediction model where at 3 weeks before harvest you can pick 100 apples from a block and put them in a crate at room temperature. In 21 days, check for bitter pit. https://rvpadmin.cce.cornell.edu/uploads/doc_855.pdf. This might be too late for this year, but I'll mention it anyway.
