How long have they been in the ground ? What is your general location ? What was previously planted in that spot ? Have you applied fertilizer ?

They've been in the ground exactly one week today and I haven't planted anything in that spot before. I have not applied any fertilizer either. I purchased some Miracle-Gro all purpose plant food but I haven't used it yet because I didn't want to over water in case that was the issue. I'm located in Texas in zone 8a.

Hmmmm ... has it warmed up there yet ? What are the highs and low's now ? I'm trying to isolate if conditions are conducive to fungus right now and how much water it's using and how much water is evaporating, ... but my first reaction was over watering. In the ground a week and with that organic mulchy stuff around the base, my guess (without knowing how warm it's been or the drainage properties of your soil) is that it should have been watered thoroughly the day you planted and once after that, maybe twice . How many times have you watered it ?

The other thing that concerns me is that my experience with Bonnie plants is like anything else mass produced ... quality control just isn't there, and these things usually show up at Home Depot or K-Mart , often sick off the truck, where the garden area is often neglected as compared to a real nursery ... and it winds up being a giant petri dish full of funky diseases from various other regions since these plants are from all over.

Looks like mildew.

The weather has been a bit odd here lately, warm days followed by suddenly cool temperatures but on average we're getting days with highs of mid 80's and lows of mid 40's -50's. I've watered the plants three times now. Once when they were originally planted and once every other day afterwards because the soil felt dry about an inch and a half to two inches below.

I've grown all kinds of melons for years and mine have never looked like this, so its tough for me to identify. Sure doesn't seem like you would have drowned them already based on your watering. If they were mine, I would snip off the damaged leaves and dispose of them far away from the garden and operate on the premise that this must be a mildew/fungus. I'd spray Bonide's copper spray on the tops and bottoms of the leaves and mist the soil immediately surrounding it, then again in 3-4 days ... be advised I go nuclear fairly quick though when things look sick ... a more subtle/organic approach might be neem oil on the tops and bottoms and all around.

Thank you so much for all your help, I truly appreciate it! I might try the neem oil and see how that works out.

No problem ... spray when the sun is fading late afternoon or early evening ... certainly not with any kind of warm sun shining on them.

You planted the melons too soon, and they're having a hard time adjusting to the wide temperature swings. The soil temps are also not as warm as they need. You may need to replant, once your temps get consistently warmer.

That's a good point rayrose makes ... made me remember the first year that I planted melons ... got excited and planted them too early ... wound up yanking and replanting once it warmed up consistently. Mine didn't get sick though, they just kinda sat there stunted and the bugs chewed them up. Here in zone 9B Northern, CA, I now know to not plant melons before May 15th'ish.

So what have you decided to do ?

I bought the neem oil and sprayed all the melon plants but I think my issue was not watering enough. I'm going to see how that works out but I've started some plants just in case. I've also bought a fish fertilizer to use on them.

Ok, was wondering. Yeah I think the underlying issue is its a little early and the cold with big swings made them vulnerable to various things. Melons are tropical plants, they like consistent warm temps. Anyways, I was going to suggest direct sow, but sounds like you may have put seeds in starter pots. The way I plant melons is on a mound, direct sow 6-8 seeds and keep the strongest 2-3 and snip the weak ones. The mounds help the soil get warm faster and helps with drainage. After the weather gets warm, I mulch to keep in moisture and protect the roots from too much heat. Also, melons don't like being transplanted, the roots are very sensitive ... although I have carefully transplanted with success, direct sow has been much better. Also, any disturbance or interruption early on can really stunt them and affect production down the road ... and its too late once you realize it. My first year of melons was a train wreck.

I’m in Dallas and experiencing the exact same thing. It’s probably weather related. Highs in the mid 80’s followed by highs in the 40’s and evenings at 34-39F followed by nights in the mid 40’s consistently is just wrecking havoc on those plants and mine as well. My cantaloupe 2 in babies are toast now because of that same reason.