My husband and I are travelling to Cambodia for one week, in the first week of July, we will be staying in Siem Reap and Phnom Penh. Should we take Malarone for Malaria or is using a spray containing DEET enough? Is July the rainy season?

According to the CDC, SR is in the malaria zone. I was advised to take prophylaxis by my travel doctor.

You need to put on DEET consistently. I used 23% DEET and occ forgot to reapply. I got bites then but fewer than those who forgot completely. Also make sure you get all exposed skin. I forgot my sandaled feet and fingers. Got a bite between the straps and at the base of two fingers. The mosquitoes are ferocious.
July is wet season, dengue fever risk. SR most definitely has dengue fever. Dengue fever mosquitoes are active in the daytime, malarial evening and early AM.

nibblette is quite right. If you follow the recommendations of the cdc or the WHO you need both - an anti-malarial and deet to prevent mosquito bites.

Thanks for the info, I think we will give Cambodia a miss in July, not keen on the Dengue Mosquitoes, we will go another time as we are keen to go but we obviously need to pick a more suitable month.

I recommend December. We took Malarone, but didn't see one mosquito. And the air temperature was perfect.

If you are making the decision purely on the basis of dengue, note that there is dengue fever in much of SE Asia and even in Hawaii...