I'm not knowledgeable about what type of plastic John Deere hoods are made from.
If.......the hoods are made from one of the "poly" plastics, there is no kind of "solvent weld" or "solvent bond" product that can be used.
If the hoods are made of ABS plastic or some variant in the PVC family, there are some exotic "solvent epoxy compound" repair kits that can be found in the plastics supply industry.
A test to determine whether plastic is a candidate for solvent epoxy repair can be done by using a solvent based cleaning product on an inconspicuous surface of the item in question (like the underside of the hood in this case).
Use lacquer thinner or acetone (nail polish remover) on a rag and wipe the surface vigorously. If the surface becomes tack, sticky, or imparts some of the item's color onto the rag, the item is a candidate for solvent epoxy. If the surface of the item stays glossy and does not become tacky or sticky, it can't be repaired using solvent epoxy compound.
And the solvent epoxy compound I refer to is not your run of the mill epoxy product like JB Weld or any number of similar products found in home improv stores. The solvent epoxy compound is a specialty product that you may only find in comprehensive plastics industry supply houses.
If the hood is made from one of the poly family plastics, you might even find an identifying code molded into the underside surface of the hood. These codes are to identify the plastic for recycling purposes when a component is disposed of.
The code may be shown as HDPE and include the numeral 2 in the center of the coding emblem, or it may simply be the numeral 2 in a few spots. If you see HDPE (high density poly ethylene) anywhere on it, you can forget about solvent based or epoxy based repairs. Solvent will not attack it and epoxy will not adhere to it.
If it is poly, your options are either hot air welding (done by a professional in the trade) or by shaping sheet metal patches/overlays/underlays and attaching them with machine screws. Neither will be a pretty sight. Actually, no kind of repair would be a pretty sight but I doubt we are looking for show quality results. More like keeping the hood shaped somewhat like a hood and mostly in one piece :^)

TPO plastic

3M Automix 5895

You could buy a new hood, "Green Parts Store" has one for $214 - see link. Or search for a cheaper one.

Here is a link that might be useful: Hood

If it is the 3m automix, there are repair kits out there (and they ain't cheap). See video in link below.

Here is a link that might be useful: Link to 3m automix repair

The Hood is listed as made of Xenoy . See the link below for it's specifications

Here is a link that might be useful: Xenoy

Thanks for all the responses. It's great to be able to get answers and solutions to problems.

I guess the hood repair options have now been eliminated. Yesterday, I took my JD X300 to a welding shop for some deck repairs. The driveway to the guy's shop was rutted and apparently the tie-down strap had come loose. The tractor bounced forward, hit the front of my trailer and demolished the green part (most) of my hood. Now it looks like a big jigsaw puzzle.
I just wonder what genius at John Deere decided that it would be a good idea to start making tractor hoods out of plastic. I will think long and hard before I ever buy another tractor of any type or brand with a plastic hood!

I have not investigated it, but I suspect you will have a long search to find a tractor that does not have a plastic hood. Plastic has replaced many of the parts that use to be made of metal.

I have a John Deere 4400 and it has a flimsy plastic hood which I have had crack on different occasions and I ALWAYS use JB Weld and it bonds very well and is easier to use ,if the hood cracks again I can assure you it is not the JB Weld that cracks it is a new crack elsewhere in the hood , the older tractors like mine circa 1999 ,2000 have a less impact resistant plastic then the newer tractors of today. I have had the hood crack if the hood was dropped and instead not carefully closed . The hoods for John Deere today it appears they are mixing a thermo plastic rubber in with the plastic when the hoods are molded , this is called impact plastic I can see a HUGE difference on my new John Deere X 758 Signature series as compared to my old JD 4400 in quality and flexibility. As far as ALL tractors having plastic hoods this is not true , the Massey Ferguson tractors at least the larger ones I know have a metal hood.

Which JB Weld did you use? They have quite a variety of them.

I have a JD LTR166 which had a crack in the hood near the hinge and the hinge was broken I used J-B Weld PlasticWeld Epoxy which is holding up well. For the hinge repair I found that the plastic cupped

washers that hold standard bed heads on fit the round hinge section of the bumper perfectly so put a bolt through it and epoxy it to the hood. It works great.