May be it is excess of water causing bad soil aeration.

If you dig small soil pit (to a depth of about 50-70cm, you can check, if it is possible to see many grayish, greenish or blue spots coevering about 40-50% or more of soil volume (or surface of the wall of the soil pit). It could be interesting to measure redox potential of soil.

If it is confirmed, that the water excess causes the problem, it will de necessary to drain the soil in future plantations (however, the drainage of heavy soils is not very efficient due to low hydraulic conductivity of theses soils) or at least dig greater pits when planting fill them with mixture of  soil and compost or other kind of organic matter. Organic matter improves drainage of clayey soils.I hope it may be helpful.

The CTAHR literature points to the root restriction and the clay soils holding excess water. Papaya needs good porous soils for drainage. I suspect you know this. Are you referring to powdery mildew ? Age of tree does  not appear to be a factor.

Could pH be playing a role as well?

At least there are good researchers in that field at CTAHR. This sounds like an extension question.

Good luck.

Patricia

 Powdery Mildew of Papaya in Hawai‘

 Plant Disease

 Brennen Cunningham1 and Scot Nelson2

1Department of Natural Resources and Environmental Management

2Department of Plant and Environmental Protection Sciences

July 2012

PD-90

PA, C. F. S. (1989). c. L. Chia, Extension Specialistin Horticulture M. S. Nishina, Extension Agent, lllTAHR, Hawaii County D. O. Evans, Research Associate in Horticulture Family: Caricaceae Scientific Name: Carica papaya.

Hi Deon,  raised beds are a strategy to avoid this.   In the clay soil of my suburb the paw paw trees just come up by themselves within the raised beds we have around the yard.

Happy New Year!  

Julie

Pythium like fungi are difficult for papaya plants on tight soil. Work in Hawaii Ko is the researcher shows the when Calcium is sufficient the rate of decay is much less.

When dealing with Papaya it is good to start your plants in a medium that has about 50% sand 25 soil and 25% mature compost.

Make sure not to over water. In your planting spot create a raised bed to favor drainage and amendment you plant area with sand and mature compost. There are some fungicides that can be useful but it is critical not to over irrigate. In relations to your soil get a soil analysis and make sure the mineral composition is optimized. 

I think, that raised beds, as suggested by Julie and Paul I the best way to resolve problem, actually it is also a kind of drainage, most efficient in such situation. I suppose that a water is not a limiting factor in that area.

I also think overwatering the trees was the main cause. Always observe the soil moisture content using tensiometers before watering. Always 60-65% allowable water should be good to support seedling growth. In heavy soils, this could be lower, probably 50% or less but also the evapotranspiration rate of the crop should be looked into.

FYM +Zn+K should be supply during application of water. They act as soften the soil. Generally heavy soil restrict the root growth and its function. So, through this practice wilting issue can solve. While fungus can be control through application of fungicide application from soil and over the area where fungus extend. Important is that drought should be created in root zone of papya after each application of FYM+Zn+K during water.  Some time excessive moister also cause fungus growth.

Pythium and Fusarium are major organism cause Papya wilting, soil tratment with fingicide may be best solution, or if you inoculate soil with B subtilis cuture which also shows anatagonism and stops fungal spread

Satish