Observations from the field

The warm to hot conditions have prompted me to think about the PET (potential evapotranspiration) situation. From memory, this is the amount of water that a short extensive well irrigated crop will use in a day. I also remember the clothesline effect which is where plants ‘sticking’ up in the air use more water than a grass paddock. Our portal is suggesting that about 6mm will be used per day in the next few days in Hawke’s Bay, which reflects what has been used in the last few days. So, a week of this could well use 40mm of water.

Jack Hughes from Fruition tells me that their monitoring service is suggesting that light soils are at 50% RAW (readily available water), medium textured soils 60% and the heavy soils at about 75% RAW. The dairy farm that I do some work on is also gearing up to begin irrigating. Common sense and some measuring in the same space – good! So, that 100mm of rain from the middle of last month is being used up and trigger points for irrigation are approaching.

Cromwell and Clyde forecasts are suggesting PET of 4mm plus per day. Alexandra has had a few of these hot days and not a lot of rain recently, so on the light soils it could well be worth checking the soil status. These numbers can be found in the regional forecasts in the Tools section of the portal.

With some more rain or irrigation, I’m now thinking of brown rot. Plant & Food Research has confirmed that ‘after pit-hardening thinned fruit can be an important source of brown rot inoculum’. And we are seeing plenty of fruit being thinned at present. My monitoring of pit hardening is that for apricots this has occurred and that other fruit types it is occurring now (first week of November).

A Google search backs up Peter Woods work:

Green fruit are susceptible to infection prior to pit hardening. With peaches, nectarines and plums, early infections may remain quiescent until the fruit ripening phase when they develop into visible rot symptoms. After pit hardening, green fruit are generally not susceptible to infection by the brown rot fungus. However, brown rot can occur on green fruit when they are:

    • thinned after the pit hardens and left on the ground
    • injured by insects, hail, birds, or by other means
    • freeze-injured or stunted and remains on the tree.

Brown rot on green fruit is a serious problem, because large amounts of fungal inoculum can be produced on diseased fruit. The inoculum produced may spread and infect ripening fruit.

Authors: Elizabeth Bush and Keith Yoder, Virginia Tech, see https://wiki.bugwood.org/Monilinia_(brown_rot_of_stone_fruit)

That leaves me the final thought and probably the point of this note; raking out the thinnings and mulching them to speed breakdown would be a very good idea.

Richard Mills