Plant has curved over. Need help in straightening it out.
You might try to tie it up, attached to a tall stick. Old nylon stockings or tights are good for this as the tend not to damage the plants and will give a little. As they lift up just keep moving up the stick until they eventually straighten out.
Thanks that makes lots of sense and I can use those for other plants. Will try.
I totally agree with what Joy suggested, gradually straightening it up is the best way to straighten it. It will keep it from breaking by trying to straighten it too much at once. Give it time and you should have it pretty straight. Keep it going on the stick, even though you get it straight, it may just be the weight is a bit much for it to not want to bend. Sometimes they also will start bending because it is reaching towards light coming from a nearby window, if that is the case, rotate it every few days a bit so that it will get sun on all sides over the week and it may not try to bend to the light.
I think you need to transplant it in a larger, deeper pot first. Then see how you can straighten it up. Looks pot bound to me
This diffenbachia is not at all dumb. It is simply trying to put it's leaves where they will get more light. It doesn't need direct sunlight, but it would benefit from being moved to a location with more light. This stem will not straighten, as it is too mature, but other stems will grow straighter, if the light that they received comes from above them. This stem will continue to grow toward its light source, so may turn and grow upward after you give it light.
First transplant it to a pot with drainage. The plant is suffering from too much water remaining in the pot and drowning the roots. Use new potting soil with lots of perlite or sand. This allows water to drain faster and leaves more space between the particles of soil for oxygen. You can put the pot with drainage inside of a decorative pot, or on a tray that will catch any extra water when you water it. Be sure to pour out water that collects in tray or pot. This plant would have more healthy foliage if the roots had access to more oxygen.
Probably grew toward the light early on. I'd cut the central stalk close to the bottom of where the leaves emerge, making sure you have a few nodes at the bottom, and either root it in water and then plant OR treat it with some root hormone and replant so it stands straight in a clean pot with fresh soil. You might need a stake til it roots securely. Cut the curves away from the remaining stalk which can be left in pot to re-sprout new leaves. Theoretically, leaves (or roots) can grow from any node, so you can cut up the stalk in a few pieces to pot with the bottom rooted piece to "fill in" the look for a bigger plant. Dieffenbachia like no direct sun and bright to filtered light in the house and if you have no pets, you can feed a little diluted fish fertilizer once a month. Looks like your watering schedule is good! Do wear nitrile gloves and wash well after cutting up the plant as the juices are toxic. So hopefully you don't have pets or young kids at home.
If it is as thick as photo shows there probably isn't much you can do to straighten now. You may have to cut it off and reroot in water. Plant the re-rooted piece in pot with a stick to first guide it straight and turn the pot as it grows a 1/4 turn each time you water it. It was growing toward the light supplied. It seem too thick to try to straighten now without breaking it. Cut below the bend, peel off all leaves that will be submerged and put it in a jar of water until long new roots have formed. The old plant should survive and start it out straighter by the same means leaving it in the pot until it grows new leaves. Stake it as well and allow it to grow up the stake in a straight position with plant ties. The are wire with soft rubber around it to not cut into branches of plants. do not tie them tightly but make a loose loop or you will hurt the plant.