Apr 3, 2020Take care with postharvest cantaloupe, summer squash
Cantaloupe and summer squash are important cucurbits in the Southeastern U.S. but how they’re handled postharvest is key to shelf life and quality.
For cantaloupe, poor handling is the No. 1 cause of postharvest quality loss. “A wound could be an entry point for any number of pathogens,” said Tim Coolong, University of Georgia (UGA) Extension specialist and associate professor in the Horticulture Department.
Injury will also increase ethylene production in the fruit. Ethylene is an essential part of ripening for Eastern cantaloupe (muskmelon) but it does decrease storage time. “Ethylene can increase softening and that could be a problem,” Coolong said.
Coolong spoke on postharvest handling of cantaloupe and summer squash at the recent Ag Expo in Wilmington, North Carolina. Ag Expo is jointly presented by the North Carolina Vegetable Growers Association and the North Carolina Agribusiness Council.
Ethylene levels increase in cantaloupe as they ripen and that ripeness determines the harvest window. “If the cantaloupe are harvested a little before half slip, you’re probably OK in terms of storage,” Coolong said. “If they’re left out in the field much longer, the fruit doesn’t hold up as well or ship as well. By the time it gets to its destination it may get a little soft.” Slip refers to the slow separation of the stem from the fruit as the fruit ripens and is used as a ripeness indicator. Growers can harvest later than half slip if selling to a local farm market.
Environmental conditions at harvest also affect the firmness of developing fruit. Warm and dry weather is ideal and leads to a ripe fruit with low disease risk. Weather that’s too hot can cause sunburn and lots of rain can exacerbate the effects of poor handling.
If you do end up with poorly handled cantaloupe, separate them from the rest. Putting damaged fruit into a bin of good fruit could reduce the quality of the whole bin.
Rinses with a bleach solution postharvest or a later treatment with ozonated water to remove pathogens are always a good practice. “Ideally, you’d be targeting any E. coli or salmonella that could be a human pathogen,” Coolong said.
Food safety is paramount with postharvest handling. “Our growers are very careful about how they handle the fruit,” Coolong said. “Food safety is a top priority of our growers.”
The Eastern Cantaloupe Growers Association (ECGA) is a voluntary organization that has the goal of delivering the safest cantaloupe possible to the consumer. The ECGA at ecga-usa.org has a number of vigorous, food safety protocols in place for participating growers. The list includes environmental testing for pathogens, the testing of all water sources, prohibiting the use of porous materials such as carpet or wood that could contact the fruit during handling, to name a few.
Organic matter or soil on the cantaloupe at harvest can reduce the effectiveness of postharvest rinses. “If the fruit is off the plastic and you get some rain, the cantaloupe can have soil on them,” Coolong said. The issue is more problematic on fine-textured soils and less likely on sandier soils.
Calcium is sometimes considered as a postharvest treatment. “Calcium treatments for fresh cut melons will increase the firmness of the cut pieces and can extend shelf life,” Coolong said. “On intact melons, there’s little research to show it’s that effective.”
Some good, long shelf life (LSL) varieties are available but pose challenges at harvest. These varieties don’t slip, so workers may have to check the netting pattern or color change to verify ripeness. “In Georgia, we don’t have a lot of acreage of LSL varieties but when we are able to harvest at the right time, they have done well in terms of yield and sugar content,” Coolong said.
There are some clear varietal differences in how well cantaloupe store.
“Absolutely we have seen a difference in eastern melons versus LSL,” Coolong said. “Most of the Eastern melons are pretty similar, but even in Eastern melons, we have seen some differences in storage.” In general, the newer varieties store better than older, established varieties.
Summer squash also has handling issues at harvest than can affect storage quality and weather is the dominant factor. Wet weather brings on disease and phytophthora is clearly the most troublesome.
Visible symptoms of phytophthora will generally show up soon after infection but there is a delay. This means the fruit can look fine at shipment but be rejected at market.
Phytophthora is so weather dependent, there are few control options at harvest. “It’s best to manage phytophthora during the growing season,” Coolong said. This can be longer rotations, selecting fields without a history of the disease, ensuring good drainage and using protective fungicides.
Choanephora rot is an occasional problem on summer squash and also shows up in extremely wet weather. Diseased plants are generally clearly identifiable and workers can avoid harvesting from infected plants.
Swollen lenticels on summer squash may also be related to very wet conditions and result in rejected squash. The issue is highly variable and may show up in one picking and then go away.
A recent UGA study on the softening and appearance loss of summer squash varieties showed some surprising differences between straightneck squash and crookneck squash. The goal of the study was to determine at what threshold the fruit became unmarketable.
“Straightneck squash stayed firm for 10 days but over time it’s color darkened and the fruit became unmarketable,” Coolong said. “Crookneck looked good for about a week, but then firmness dropped off to where it wouldn’t have been marketable.” The larger bulb at the end of crookneck squash is probably why it softened faster.
The bleach rinse of wet pack summer squash helped them hold up better in storage than dry pack. “We found that rinse really firmed up the fruit,” Coolong said.
Some varieties in the study got a little darker in storage and may have reached unmarketability, but other varieties maintained color. “That was something that really stood out to us,” Coolong said. “It’s back to that message of choosing the right variety for your system.”
— Dean Peterson, VGN correspondent