The ABCs of PGRs in vegetables

According to our 2014 State of the Industry Report, 43 percent of growers project edibles to be the category with the biggest increase in production this year. Greenhouse Management recently spoke with T. Casey Barickman, Ph.D., about the use of plant growth regulators (PGRs) in vegetable transplant production. Barickman is assistant research and extension professor at Mississippi State University, and his research is in small fruit and vegetable production with an emphasis in plant physiology and nutrition.
 

What are the most important considerations before treating greenhouse vegetable crops with PGRs?

The most important consideration when using any PGR is to read the label. Make sure the PGR is labeled for use on the crop you are treating. The last thing you want to do is to apply a PGR that is not registered for use in a particular crop. The plants could have a negative growth response or even worse, you would not be able to sell it to consumers because it was used off label, which is against the law. Using PGRs off label could also make someone ill.

Another important consideration is safety. Make sure you have the proper personal protective equipment before handling the chemical. Most PGRs must be applied by a trained and licensed employee. Personal protective equipment (PPE) is the first line of defense in protecting the person from the PGR exposure. The label will disclose what PPE a person needs in order to apply the PGR. Furthermore, you want to have in mind how the end product is going to be affected by the PGR because you want be able to sell a quality product and a lot of it.
 

What are some of the benefits of using PGRs on vegetable crops?

Sumagic, a gibberellin, is the only registered PGR that can be applied to greenhouse vegetables for transplant production. Sumagic is used on transplants to control height. Growers that encounter adverse environmental conditions, such as high temperatures and high/low light intensity, may need to apply Sumagic in order to keep the plants from having increased stem elongation. Having the option of applying a PGR to control plant height can make the difference between profiting and losing money on your product.

There are many other PGRs used on vegetable crops for field production. For example, the PGR ethephon is used in cucurbits to increase flowering. Other PGRs are used in vegetable production for expression of female flowers — especially in cucurbits — induction of flowering, hybrid seed production, increased fruit set, and fruit ripening. If you would like more information on PGRs use in vegetable production, contact an extension vegetable specialist in your state.

In the near future, I am hoping to see more PGRs registered for greenhouse vegetable crops, especially PGRs that can affect fruit quality and yields. We are working on a few projects with experimental PGRs in my research program at Mississippi State University. We are examining how they can increase nutrient acquisition, decrease physiological disorders and improve fruit quality and nutritional values of vegetable crops.
 

Which class of PGRs is most effective for use in vegetable crops and why?

This question is hard to answer because it depends on what a grower is trying to achieve in a particular vegetable crop. Classes of PGRs include auxins, gibberellins, cytokinins and ethylene generators, to name a few. They all achieve a different response in plants and are used for different applications. Activol and ProGibb are gibberellins used in vegetable crops to increase size and fruit quality. For example, Activol can help promote early growth in tomato plants, which is especially important when low temperatures are expected early in the spring season or late in the fall before frost. It breaks dormancy and stimulates sprouting in seed potato production. In addition, ProGibb can help facilitate harvest, increase yield and improve quality in collard greens and spinach. In cool weather, it can help vegetables such as cucumber and pepper to stimulate fruit set and promote early season growth.
 

Have you seen negative effects on vegetable crops with PGR use?

Negative effects of PGRs are usually induced by some type of user error. Applying PGRs on unlabeled crops will mostly likely give a negative response. Other errors are miscalculating concentrations that are applied to the greenhouse vegetable crop and/or using too much of an additive such as a surfactant. This can cause burning of the plant tissue (roots/leaves) depending on where it is applied. Applying the PGR at the appropriate stage of plant growth is important to avoid negative responses.
 

What are the most effective treatment application methods (seed drench, soil drench, spray etc.)?

There are many application methods to effectively use a PGR treatment. My best advice is to consult the PGR label for the best application method. There has been extensive research and data to support what is on the label and the person applying the PGR should always follow the provided information.
 

What safety concerns exist when using PGRs in edible crops?

The main concern using PGRs is in edible crops for greenhouse applications are that there is a lack of research and data to guarantee safety in a controlled environment. We need more studies that demonstrate efficacy of a desired outcome, whether it be flower formation, increased fruit size or improved nutrient uptake. In addition, because the applications of PGRs will be in enclosed controlled environments, I think we need studies that look at the retention of residues to the leaves and fruit of vegetable crops. This could raise a red flag for safety, especially when customers consume fresh vegetables that have been treated with PGRs.
 

In which vegetable crops do you see the biggest positive impact of PGRs?

Since there are limited PGRs for vegetable transplants I see the biggest impact on summer vegetables transplants such as tomato and pepper. However, I am hoping in the near future we will have more registered PGRs for applications to greenhouse leafy and fruiting vegetable crops. I would say the greenhouse vegetable crops that would benefit the most are tomato, pepper, cucumber and lettuce because these make up a majority of the greenhouse vegetable market.