We’re living central Haiti at 1500m. One of the predominant crops in our area are sweet potatoes but it’s our assessment that there is a lot of room to improve yields here. Sweet potatoes are so suited for our climate that they actually grow as weeds here. Once a field has been planted in sweet potatoes it will always have sweet potatoes.
One problem that we’re having is that a certain percentage of the roots are infested with a mystery disease. I have seen any insects. When you cut into one of the sweet potatoes it’ll have black streaks throughout it. If you happen to cook one by accident it VERY bitter and tastes incredibly toxic. Our neighbours’ sweet potatoes have the same issue. The picture below is of a particularly bad sample.
Thanks for sharing photos. I have an initial thought based just on the pattern on the damage but photos of any lateral roots and the outside of the tuber would help confirm or deny my thought. Do you have any photos of the roots and of the outside of the tuber?
I don’t still have this particular sweet potato. I actually took this picture a few months ago when I found this particularly bad specimen. I will keep my eye out for another one that I can take a picture of. I can say though that I have not been able to identify good sweet potatoes from the bad without cutting into them. With some batches that we’ve bought from neighbours we’ve had to cut into them all rather than boiling them whole just simply to avoid getting a mouthful of bad sweet potato.
I have noticed recently that some of the leaves that are growing on various plants around our place seem to be infected with something. I don’t know yet if there is a correlation with the bitter root problem but I’ll put a picture here. It might be a red herring though. Also some sweet potatoes seem to develop a waxy, black coating that I usually peel off but again I haven’t correlated that with the bitter taste. I can also try to add a picture of that here when I find it.
To be honest, the first photo you sent reminded me strongly of what root-know nematode damage looks like on the inside of banana corms when you cut them open, but if you don’t see scabby lesions on the surface of the sweet potato tubers, I don’t think it could be caused by RK nematodes. They need an entrance into the tuber and would leave a mark on the outside. From what you are describing, I do think that it’s a soil pest/pathogen and that the leaves you photographed are a separate issue (not a bad one by the looks of it as it is affecting <30% of the leaf surface).
I’ve recently connected with some of the sweet potato experts at CIGAR trying to ID a variety in Central Africa. I’ll ask them to look at your photos to assit with a possible diagnosis!
Thanks for getting back to me. This is interesting. I took a look a RK nematode damage on sweet potatoes and I agree that that’s probably not my issue. I’m looking forward to hear back from you if you get any further clues.
On a different topic, I’ve been researching ideas to control weevil damage. We have no end of trouble trying to save seed from corn, beans, or millet. Our neighbours that are actually bothering to save seed are using a pesticide that they can buy locally. We want to figure out a working solution so that we can help our neighbours find a better way. I looked through a bunch of your previous experiments and discussions of the web. I also got a bunch of suggestions from an online discussion forum. Have you seen this study: https://www.sciencedirect.com/science/article/abs/pii/S0022474X18300407 ? Also, how do I light a candle in a bucket without melting the plastic lid? We put a candle in a plastic water barrel 3/4 full of corn and even that candle started to melt the lid. Maybe that was because it had enough oxygen in the 1/4 barrel of air to keep it going long enough to start melting the lid. I’m just a little leery of risking my bucket lids. What is your current weevil recommendations?
Do they sell PICS sacks there for grain storage? They were developed by Purdue university especially for grain storage.
They are essentially just 2 large transparent clear plastic bags placed inside of each other and inside a normal grain sack. (3 in 1). One fills them, knots the top of the inside bag, then does the same with the second… folding the plastic over itself as you knot it. The whole point is to keep it airtight.
Anyone tried with garbage bags?
Still check your grain once a month.
Protect from rodents… If they chew a whole in the bags it’s all a waste of time as air can get in… Those sacks are very common in West Africa, affordable and widely used. I recommend them for weevil protection.
Also they avoid the use of chemicals… Not that all chemicals are bad or that. They don’t have their place but if I can avoid them - I prefer to.
If I’m not mistaken there may be other threads about them.
Try googling sweet potato disease identification guides - they exist and might help you - they are what agronomists would use to help you diagnose it. Have you asked the locals? Do they have a name for it? Are their local or regional agronomists that have WhatsApp?
You mention the lack of rotation in their farming.
At school they taught us that each year you don’t plant a crop in field the pests and disease that target it reduce by about 50%.
A corn and soy farmer from the USA once told me what a big difference rotating made when they started… they do 2 years corn, 1 soy but it really helps.
How come they don’t rotate the cropping? What are the other crops they could grow or rotate with?
Also - have you quantified the yields? I encourage you to- measure the yield per square meter and extrapolate to per hectare or acre.
Also, try and quantify the amount of damage the disease is causing.
