Many of the diseases that affect the commonly grown vegetables in this neck of the woods are only threats if they can find a way through the physical armour that is the skin of the vegetable. Vegetables that are healthy and unstressed, and that have intact skin, are much less likely to become infected. At the same time, a damaged skin or tissue is an open tap for water to be lost from the product, which accelerates post-harvest decline and reduces post-harvest quality and lifespan.
As a vegetable grower, are there any strategies that can be employed to tip the balance in the favour of the vegetable? Unfortunately, there is really only one overarching strategy. If you want to thwart successful attacks by pathogens, and to reduce water loss after harvest, preserving and maintaining the skin of the vegetable is the best strategy.
In my mind, I’m mostly picturing potatoes since they tick all the boxes when it comes to the relationship between an intact skin and reduced losses due to disease or water. But the principles apply to most vegetables, including bulb vegetables, as well as winter squash and pumpkins.
Strategies
The first side of this strategy is the careful handling of harvested products. If you can avoid damaging the product as it is picked or dug, that is a great start. If your product has to be harvested mechanically, make sure that the harvester (and any equipment that is used to move product around after harvest) is properly calibrated and is operated correctly. Avoid excessive drops or slamming the product around. Don’t throw things around or bang them into things. While we might think that a wound has to be a cut or gash, in reality, a bruise is a significant weak point.
Another angle on the overall strategy is to encourage the crop to dry down and tighten up the outer layers as much as possible before trying to store them. Bulb crops like onions and garlic significantly benefit from lifting and drying and then some extended curing. By waiting for the tops of the crop to start to fall over and then lifting them out of the soil, you encourage a natural drying down and tightening up. Putting the bulbs into a warm, dry area for a period of time will tighten up the neck tissues, essentially sealing off that area from moisture loss (and disease attack). The dry outer scale leaves are less easily attacked and protect the tender inner tissues.
Potatoes will toughen up their skins once their tops start to die down. If you kill the tops artificially, by mechanical or chemical means, you can trigger the same process. It is important to wait 2 weeks from the tops being killed before harvesting, otherwise the skins are still thin and tender, and the likelihood of scrapes and scuffs is much higher.
Some crops also have the ability to repair and replace damaged tissues if given half a chance. Potatoes will start to lay down tough layers within a very short time of tissues being damaged. These reinforced suberized layers seal off inner tissues from moisture loss and attack from diseases. If you give potatoes a few weeks of warmer conditions in storage before slowly dropping the temperature each day, this curing period will help potatoes to heal up any wounds. This will cut down on water loss later on.
If you give squash and pumpkins a bit of a curing period after harvest, they can toughen up their skins somewhat, and dry up any superficial wounds. Some people rub honey on pumpkin wounds to help with healing, but I’ve never tried it. Giving them a bit of a wipe with a disinfectant can also remove any surface pathogens, hopefully preventing post-harvest infection.
The moral of the story…
The overall message is that it is critical to do whatever you can to help vegetables preserve their skins or repair any gaps. Work to prevent injury and then give them a chance to heal if that is a possibility.