Guinea fowl are generally much easier on your plants than chickens but you can not use pest sprays when you have guinea fowl as you may poison them.
They do so much wandering they will find all sorts.
1. Chocolate or caffeine.Both are fatal even in small quantities.
2. Never let your chickens to eat dried lentils or raw beans.Beans need to be heat treated or roasted. They contain a toxin called phytohaemagglutinin which is fatal to humans in surprisingly small quantities let along guinea fowl. Don't let them into a vegetable patch where beans are going. as few as 4 beans can kill.
Dried beans are known to create very serious illness and even death in adult humans and poultry, they are always fatal. Kidney beans are the worst culprit but any bean which has not been properly cooked is potentially lethal for your Guineas.
Once eaten, there's nothing to be done to save the bird.
3. Rhubarb and Avocado.Avocado's contains persin that's poisonous to chicken and the things are way expensive so why bother. Rhubarb contains Oxalic acid which can make them feel really unwell for a long time and give them soft shelled eggs.
4. Too many scraps.I once saw this summed up brilliantly in a poultry book from the 1860's. The author said " If you have a lot of scraps from the kitchen you probably need to look at how you are feeding your family"
Bread is not good for poultry and feeding kitchen scraps to any livestock is illegal in most parts of the west.
5. Green tomatoes or potatoes or uncooked potatoes.They are members of the deadly nightshade family.
6. Guinea fowl should not eat any mushroom, mouldy or fungus.
Spores can germinate in the crop, stomach and intestines and release toxins that kill in very small amounts.