It is unfortunate and we feelsorry for the bad incidence.
Since you want to follow, Zero Budget Natural Farming, of Sri Palekar , we are nothing to say as we are only practsing Organic farming.
Organic farming is expensive and not a Zero Budget. Since you mentioned heading as Organic remedies , we will explain, basing on our organic farming experiance.
As you are aware, in recent times, Guava plants are much subjected to Nematodes problems, all over India, and hundreds of acres are uprooted, for which, the experts opinion in Organic method is , as follows to safe guard the plantations.
Initially prepare a solution with 200 ltrs water mixed with 1 kg Trichederma Viride/Horizonum +1 kg Psuedomonas + 1 kg Paceilomysis + 1 kg PSB + 1 kg Azo spirillum/bacter , mix well and drench it in all the Guava plants pits immediately. This is sufficient for 1 acre and costs you around rs 350/- to rs 600/- per acre.
2 nd: keep one tractor load of FYM in a shade place and spread it to a height of 1.5 ft. On the above spraed 100 kgs of Neem cake , mix it well and put sufficient water only( should not leach out ). Initially there may be heat in inner portion and will come down after coulple of days. Then add 2 to5 kgs of Trichoderma Viride/Horizonum + 2 to 5 kgs of Psiedomonas + 2 to5 kgs of Paceilomysis + 2 to 5 kgs of PSB + 2 to 5 kgs of A.S/Bactor, and mix well and put sufficient water ( only humid, not watery ), mix it well and cover it with wet gunny bags. Water and mix it daily and after 10 to 12 days, you will find white powder coat under the wet gunny bags.
Immediately, you spread it @ 2-3 kg per each gova pit and mix it with existing soil. This may cost you around rs 5,000/- to rs 6,000. It can be catered to around 1,000 plants. Say rs 1,000/- per acre. As per the institutions/Universities/Experts, these above two treatments can eradicate of your soil born diseases ,incl nematodes. For organic farmers, the above cost is very reasonable and effordable.
Deficiencies of what so ever will not be exists, if organic mannures are fed. sufficient FYM, Vermicompost, Neem cake, Jetropha cakes may be provided, if wants to follow Organic method and for Palekar methods, their followers may explain to you.
with best wishes, g.p.rao, farmer